Enhanced oxygen-scavenging polymers, and packaging made therefrom

ABSTRACT

Oxygen-scavenging polymers and packaging for holding oxygen-sensitive products. A heat treatment process has been found to significantly increase the oxygen-scavenging performance of the polymer. The enhanced scavenging polymer can be effectively incorporated into various packaging, including transparent multilayer containers for beer and juice. In one embodiment, a multilayer package made from the scavenger provides an actual reduction in oxygen content of a contents of the package, over a long period of time (e.g., 24 weeks). The package can be stored unfilled for an extended period (without significant loss of scavenging capability) and will scavenge substantially immediately upon filling with a liquid product. The package may incorporate a relatively low weight percentage of the scavenger, thus providing enhanced scavenging in a cost-effective manner.

This application is a continuation of and claims priority to U.S.application Ser. No. 10/647,276, filed Aug. 26, 2003, now abandonedwhich is a continuation of U.S. application Serial No. 10/268,933, filedOct. 11, 2002, now abandoned, which is a continuation of U.S.application Ser. No. 09/745,010, filed Dec. 20, 2000, now abandoned,which is a continuation of U.S. application Ser. No. 09/241,598, filedFeb. 2, 1999, now abandoned, which is a continuation-in-part of U.S.application Ser. No. 09/236,498, filed Jan. 26, 1999, now abandoned,which is a continuation-in-part of U.S. application Ser. No. 09/169,439,filed Oct. 9, 1998, now abandoned, which is a continuation-in-part ofU.S. application Ser. No. 09/018,217, filed Feb. 3, 1998, now abandoned,the disclosures of which are incorporated herein in their entirety.

PRIOR APPLICATIONS

This is a continuation-in-part of U.S. Ser. No. 09/169,439 filed Oct. 9,1998, entitled “Enhanced Oxygen-Scavenging Polymers, And Packaging MadeTherefrom”, and of U.S. Ser. No. 09/018,217 filed Feb. 3, 1998 entitled“Solid-Stating Method For increasing Oxygen-Scavenging Rate of Polymers,And Packaging Made From Such Polymers”, both by S. Schmidt et al., andfrom which priority is claimed and which are hereby incorporated byreference in their entirety.

FIELD OF THE INVENTION

The present invention is directed to enhanced oxygen-scavenging polymersand packaging for holding oxygen-sensitive products, and in particularembodiments to multi-layer articles incorporating such polymers whichare transparent and utilize a relatively low weight percent(cost-effective) amount of the enhanced scavenging polymer.

BACKGROUND OF THE INVENTION

Plastic packaging has certain inherent benefits over glass and metalpackaging, such as light weightability, increased variability in packagedesign, non-breakability, and reduced cost. However, plastic packagingmay have greater permeability to certain gases (oxygen and carbondioxide) and liquids (water) than glass or metal; these gases/liquidspermeate the plastic and reduce the shelf life of the product containedtherein. Various specialty polymers and layer structures have beendeveloped which provide a commercially-acceptable shelf life for someoxygen-sensitive products, such as juice and ketchup.

There are two general types of oxygen-barrier materials—passive andactive. A “passive” barrier retards oxygen permeation into the package.For example, with multi-layer technology it is possible to incorporatethin layers of expensive barrier polymers (e.g., polyvinylidene chloridecopolymer (PVDC) or ethylene vinyl alcohol copolymer (EVOH)), incombination with structural layers of bottle-grade plastic resins (e.g.,polyethylene terephthalate (PET)), to provide a cost-effective barrierpackage.

In an “active” barrier package, an oxygen “scavenger” is incorporatedinto a single or multi-layer plastic structure to theoretically removethe oxygen initially present and/or generated from the inside of thepackage, as well as to retard the passage of exterior oxygen into thepackage. Thus, oxygen-scavengers are superior to passive barriers inthat they both remove oxygen from inside the package and retard itsingress into the package. However, the performance of the prior activebarrier packages is reported in terms of an overall ingress such thatthe oxygen content continues to increase over time, albeit at a slowerrate of increase than with some passive barriers.

Commercially successful hot-fill juice containers (passive barrier) havebeen developed by Continental PET Technologies, Inc. of Florence, Ky.,which provide a 1.5 to 4-time improvement in oxygen barrier propertyover a standard commercial single-layer PET container. These multi-layerjuice containers include two very thin intermediate barrier layers ofEVOH positioned between inner and outer layers of virgin PET, and a corelayer of either virgin or recycled PET. However, there are products evenmore “oxygen sensitive” than juice—e.g., beer. The taste of beerdeteriorates rapidly in the presence of oxygen and thus beer requires atleast a 10-times greater oxygen barrier property than provided by thestandard single-layer PET container. Furthermore, beer's oxygensensitivity is enhanced by increased temperature, i.e., exposure to heatduring storage has a multiplicative impact on oxygen's adverse effect ontaste. For example, if beer is refrigerated during storage and theamount of oxygen is maintained below a specified parts-per-billion(ppb), a given container may have a shelf life of 4-6 weeks (2842 days).However, if the same beer container is not refrigerated, then the shelflife may be reduced to 1-2 weeks (7-14 days).

One possible solution for highly oxygen-sensitive products is to utilizehigher barrier polymers in packaging. For example, polyethylenenaphthalate (PEN) has a 5-time improvement in oxygen barrier propertyover polyethylene terephthalate (PET). Also, PEN has a significantlyhigher glass transition temperature (T_(g)) than (PET)—about 120° C.compared to 80° C.—and thus PEN is also desirable for use inthermal-resistant (e.g., pasteurizable) beer containers. However, PEN ismore expensive than PET (both as a material and in processing costs),and thus the improvement in properties must be balanced against theincreased expense. Also, the increase in passive barrier protection withPEN does not solve the problem of residual oxygen within the package.

One method of achieving a package that is lower in cost than PEN, butwith higher barrier and thermal properties, is to provide a blend of PENand PET. However, blending of these two polymers generally results in anopaque material (incompatible phases). Efforts to produce a clear(transparent) container or film from a PEN/PET blend, and maintainstrain hardening (for structural strength) have been ongoing for overten years but there is still no commercial process in wide-spread usefor producing such articles.

Another possible solution, on which extensive work has been reported, isthe use of alleged metal-activated oxidizable organic polymers (e.g.,polyamides) as oxygen-scavengers in plastic containers. However,problems again exist with: lack of clarity; time/expense required toactivate the scavenging polymer; toxicity of the metal; need to preventinteraction of oxidative reaction byproducts with the package contentsand/or environment; and loss of the oxygen-scavenging effect duringstorage (prior to filling). For example, U.S. Pat. No. 5,034,252 toNilsson suggests a single-layer container wall consisting of a blend ofPET, 1-7% by weight polyamide (e.g., MXD-6 nylon), and 50-1000 ppm(parts-per-million) of a transition metal (e.g., cobalt). Nilssontheorizes that cobalt forms an active metal complex having the capacityto bond with oxygen and to coordinate to the groups or atoms of thepolymer. However, Nilsson notes that low-oxygen permeabilitycoefficients are achieved only after an aging (activation) process,which may require exposure of the preform/container to a combination oftemperature and humidity. U.S. Pat. No. 5,021,515 to Cochran generallydescribes the use of a PET/polyamide blend with cobalt. It suggests amulti-layer structure formed by coextrusion lamination using adhesivetie layers, wherein inner and outer layers prevent interaction of acentral scavenging layer (containing cobalt) with the package contentsand environment. However, Cochran similarly notes the aging effect.

A significant problem with blending polyesters (such as PET) andpolyamides (such as MXD-6 nylon) is loss of clarity. Most foodmanufacturers require the transparency of a PET container, and will notaccept a loss of transparency in order to achieve a desiredoxygen-barrier property.

Thus, the prior art containers typically suffer from one or more of thefollowing difficulties:

-   -   (a) lack of transparency;    -   (b) inability to process the polymers on commercial injection        molding equipment;    -   (c) only marginal improvement in oxygen-scavenging performance        over monolayer PET bottles or multilayer PET/EVOH bottles;    -   (d) aging or activation requirement to induce oxygen-scavenging        performance;    -   (e) high cost and/or toxicity.

One reference discloses that under test conditions designed toapproximate the actual conditions in beverage applications, thescavenging performance of a plastic container having a scavengingpolyamide was “comparable” to a glass bottle (see for example, thePET/polyamide blend of U.S. Pat. No. 5,021,515, example 8). In reality,plastic containers having a performance only comparable to glass do notprovide a significant incentive for beer producers to give up theirsubstantial investment in glass container bottling operations. Stillfurther, the same blend art states that with increasing concentrationsof the metal, the oxygen-scavenging performance actually decreases.Again, this would discourage one from believing that oxidizable polymers(such as polyamide) could provide a commercial container which satisfiedthe stringent low-oxygen requirements for beer.

The variety of oxygen-barrier systems disclosed in the art is strongevidence of the commercial need for such packaging, and also that theknown systems have not solved many of the problems. Thus, there is anongoing need for oxygen-scavenging polymers having enhanced scavengingcapacity and for a process to manufacture transparent articles from suchpolymers in a cost-effective manner.

SUMMARY OF THE INVENTION

In one embodiment, the present invention is based on a surprisingdiscovery that a certain heat treatment of a scavenging polymer canresult in a very significant increase in the oxygen-scavengingperformance and furthermore that this enhanced scavenging polymer can beeffectively incorporated in a transparent multi-layer container. Thisnew package provides a number of features which prior art packages havebeen unable to achieve. First (in select embodiments), it enablesproduction of a transparent biaxially-oriented container sidewall whenblow-molded (to produce strain orientation) with adjacent layers ofaromatic polyesters, such as polyethylene terephthalate (PET). Withouttransparency, the container would not be commercially acceptable.Secondly (in select embodiments), the container actually provides areduction in oxygen content of a liquid in the container over anextended period of time. i.e., exceeding 16 weeks. Such performance isquantitatively superior to that of a glass container, which shows asteadily increasing oxygen content of the liquid over time. This netreduction in oxygen content is achievable even when starting with verylow initial oxygen concentrations, such as 200 ppb or less. Thirdly (inselect embodiments), the new container does not have a significant agingor activation requirement—rather it has a high level of scavengingalmost immediately upon filling, which overcomes the prior artrequirement of an activation or aging process. Also, it can be storedempty (prior to filling) for extended periods without depletion ofscavenging. Fourthly (in select embodiments), the new containerincorporates a relatively low weight percentage of the scavenging layerwhich is helpful in maintaining transparency and in providing acost-effective container, i.e., utilizing relatively low amounts of themore expensive scavenger material.

Thus, according to one preferred embodiment, a transparent multilayerblow-molded container or sidewall of the container is formed from amultilayer injection-molded preform. The preform/container has afive-layer structure including inner, outer and core structural layersof a polymer, e.g., an aromatic polyester such as PET, and inner andouter intermediate layers of an enhanced oxygen scavenger disposedbetween the inner, core and outer layers respectively. The containerincludes a biaxially-expanded sidewall portion in which the PET layershave undergone strain orientation and crystallization for strength. Thescavenger layers can be processed at temperatures and stretch ratiossuitable for orienting the PET layers, without the scavenger or PETundergoing excessive crystallization which would render the sidewallopaque. The amount of metal in the scavenging layer can be adjusted toenhance the scavenging rate. A preferred amount of the metal is at least200 ppm based on the scavenging layer, more preferably from 200 to 2000ppm, more preferably from 300 to 1000 ppm, and still more preferablyfrom 400 to 800 ppm. Optimizing the metal concentration and wallthickness of the scavenging layer(s) and PET in the biaxially-orientedsidewall will enhance the overall scavenging performance of thecontainer.

Surprisingly it was found that the above five-layer structure enablesextraction of oxygen from a liquid product, even at initially low levelsof oxygen content, resulting in a reduction in oxygen content over time.This is qualitatively different from what occurs in a container thatmerely slows down a rate of oxygen transmission from an area of higherconcentration (i.e., ambient air outside the container having an oxygenconcentration of 21%) to an area of lower concentration (i.e., insidethe container where the oxygen content is much lower, e.g., 8000 to 9000ppb dissolved oxygen in water or juice, or 200 ppb dissolved oxygen inbeer). In the present invention, the relatively low level of oxygeninitially present in the product is actually being removed from theliquid, causing a reduction in the oxygen content. By “reduction” it ismeant that more oxygen is leaving the liquid/container than entering theliquid/container.

The prior art fails to teach or suggest this ability to extract oxygenat low concentrations. In contrast, the prior art defines the scavengingperformance of a plastic container containing polyamide/metal based on areduced oxygen transmission rate from the exterior to the interior ofthe container—i.e., based on an expected flow from an area of to higherconcentration to one of lower concentration, (see U.S. Pat. No.5,021,515, col. 3). This discussion in the prior art of transmissionfrom the exterior to the interior of the container is however consistentwith the performance of a glass container, wherein the prior art foundthe plastic container to have a performance “comparable” to that of aglass container.

Furthermore, in certain applications it has now been found thatadjusting the intrinsic viscosity (IV) and/or melt viscosity of thescavenging material will assist in providing a desired materialdistribution or wall thickness of the scavenger in a multi-layerstructure. Generally, the intrinsic viscosity and/or melt viscosity canbe correlated with a melt index for the polymer, e.g., the melt indexdefined by ASTM D1238-94a. In providing a melt index of the scavengercompatible with a melt index of an adjacent structural layer, one canincrease the amount of scavenger material which ends up for example in arelatively thin sidewall portion of a multilayer container, as opposedto a thicker neck finish portion (where less or no scavenging isrequired). For example, using a low IV scavenger, more scavenger may endup in the neck finish, as opposed to the sidewall. Adding a metal (suchas cobalt) may reduce the IV or melt viscosity of a scavenging polymer,such as a polyamide, thus further aggravating the problem ofinsufficient scavenger in the sidewall. Although it may be possible toincrease the thickness of the scavenger layer by increasing the totalamount of scavenger material, this produces an increase in cost and, incertain instances, a relatively greater percentage of the scavengermaterial ending up in the neck finish where it may not be required.

Thus, the thickness of the scavenger layer in the sidewall-formingportion of an injection-molded article (preform) may be increased byadjusting the melt index of the scavenger material. This greaterthickness of scavenger does not lead to problems of delamination, as mayoccur with prior art barrier materials such as EVOH, because thepolyamide adheres better to adjacent PET layers. Also, by increasing theamount of scavenger in the sidewall (as compared to the neck finish),other problems can be avoided, such as delamination in the finish duringblowing, and sealing defects (i.e., breakthrough of the inner polyamidelayer at the top sealing surface of the container which interferes withthe formation of a tight seal between a foil liner and the top sealingsurface of the container). Still further, there is the economic benefitof providing relatively more scavenger material at the location ofgreatest need, i.e., in the thinnest section of the container.

Thus, the following aspects of the invention may be used independentlyor in various combinations to provide an enhanced oxygen-scavengingcomposition or article.

In one aspect, a heat treatment under reduced pressure conditions isprovided which is described herein as “solid stating”. Thissolid-stating process increases the oxygen-scavenging capability of apolymer, such as a polymer having a repeat unit including a carbonyl.

In another aspect of the invention, a scavenger layer is provided whichis melt-compatible with an adjacent structural polymer layer. This maybe used to achieve a substantially uniform thickness of the scavengerlayer throughout an article or in a particular portion of an article.

According to a further aspect of the invention, a package is providedwhich enables immediate scavenging when filled with a product. Thisavoids the problems of the prior art with aging and activation.According to one embodiment, a multi-layer package is provided having anoxygen-scavenging layer consisting essentially of a polymer and a metal,the polymer having a repeat unit including a carbonyl and at least onehydrogen atom alpha to the carbonyl, a structural layer between theoxygen-scavenging layer and an aqueous-containing liquid product in thepackage, and wherein upon filling of the package with the product thewater in the product permeates the structural and oxygen-scavenginglayers and the oxygen content of the liquid product is reduced.

In another aspect a package for an aqueous liquid is provided whereinthe package has a wall comprising an oxygen-scavenging polymericcomposition, a thickness of the wall adapted to achieve oxygen removalfrom the liquid.

In another aspect, a multi-layer package is provided for enclosing anaqueous liquid having an oxygen content, the package comprising at leastone oxygen-scavenging layer comprising a polyamide and cobalt in anamount of at least 200 ppm in the polyamide and wherein the packageenclosing the liquid has an oxygen-removal rate greater than anoxygen-removal rate of a dry package.

In another aspect, an oxygen-scavenging layer comprises a polyamide andcobalt in an amount of at least 200 ppm in the polyamide, and astructural polymer layer is positioned adjacent the oxygen-scavenginglayer, wherein the structural layer is permeable to water.

According to one aspect, a method of removing oxygen from an aqueousliquid having an oxygen content is provided which includes the steps ofproviding a package having a wall comprising at least oneoxygen-scavenging layer comprising a polymeric composition, andselecting a thickness of the wall to achieve a reduction in the oxygencontent of the liquid.

In another aspect, a method of reducing an oxygen content of a liquid ina multilayer container is provided which includes the steps of providinga transparent sidewall portion of the container, the sidewall portionincluding an oxygen-scavenging layer of a polyamide and cobalt in anamount of at least 200 ppm and a structural polymer layer positionedbetween the scavenging layer and the liquid, and allowing a component ofthe liquid to permeate the structural layer to contact the scavenginglayer and cause a reduction in oxygen content of the liquid.

According to another aspect, a method of enhancing the oxygen-scavengingcapability of an oxygen-scavenging composition is provided comprisingsolid-stating a polyamide, and adding cobalt to the polyamide in anamount of at least 200 ppm in the polyamide.

In another aspect, a method of reducing the oxygen content of a volumeof a liquid comprises providing a sealed multi-layer containercontaining a volume of liquid, the container comprising at least oneoxygen-scavenging layer, the at least one oxygen-scavenging layercomprising a polymer and cobalt, the polymer having a repeat unitincluding a carbonyl and at least one hydrogen atom alpha to thecarbonyl, the cobalt being present in an amount of at least 200 ppm inthe layer, and at least one structural polymer layer positioned betweenthe at least one oxygen-scavenging layer and the volume of the liquid,wherein the oxygen content of the volume of the liquid in the sealedmulti-layer container is maintained for a period of time below theoxygen content of a same volume of the liquid stored in a sealed glasscontainer for the same period of time.

In another aspect a method for reducing a melt index of a polyamidecomprises adding a metal to the polyamide to achieve the reduced meltindex, and forming the polyamide in a layer structure with otherpolymers.

In another aspect, a method of making a multi-layer oxygen-scavengingarticle comprises providing a layer of an oxygen scavenger including apolyamide and a metal, and a layer of a structural polymer, andadjusting a melt index of the scavenger compatible with a melt index ofthe structural polymer.

In another aspect, a method for making a transparent multi-layer articlehaving an oxygen-scavenging layer comprises heating a polyamide under alow oxygen content atmosphere to increase the oxygen-scavengingperformance of the polyamide with a given metal content by a factor ofat least 1.3, and forming the multi-layer article including at least oneoxygen-scavenging layer formed of the polyamide and metal.

In another aspect, an injection-molded multi-layer preform is providedfor making a multi-layer oxygen-scavenging container having atransparent sidewall, the preform comprises a neck finish, asidewall-forming portion and a base-forming portion, thesidewall-forming portion having at least one layer of an oxygenscavenger comprising a polyamide and cobalt in an amount of at least 200ppm in the polymer, and the preform having a substantially uniformthickness of the scavenging layer in the sidewall-forming portion.

In another aspect, a method is provided for making an injection-moldedpreform for a multi-layer oxygen-scavenging container having atransparent sidewall, wherein the preform includes a sidewall-formingportion having at least one oxygen-scavenging layer including apolyamide and cobalt to provide the scavenging function, the methodincluding adjusting a melt index of the polyamide to provide asubstantially uniform scavenging layer in the sidewall-forming portionof the preform.

In another aspect, a method is provided for enhancing theoxygen-scavenging performance of a polyamide, the method comprisingheating the polyamide, and wherein a plaque formed of the heat-treatedpolyamide has a greater oxygen-removal rate when exposed to moisturethan when not exposed to moisture.

In another aspect, a transparent multilayer bottle is provided forpackaging an aqueous liquid containing oxygen, the bottle having a wallcomprising an inner layer or layers of an oxygen-scavenging compositionhaving an activity on a wet plaque test of reducing an oxygen contentfrom 21% to 19% or less in 54 days.

In another aspect, a composition for use as an oxygen scavenger isprovided which comprises a xylidene-substituted polyamide which has beentreated so that the ratio of wet to dry plaque tests when the polyamideis mixed with 500 ppm of cobalt is greater then 2:1, and more preferably3:1.

In another aspect, a transparent multilayer bottle is provided forpackaging an aqueous liquid containing oxygen, the bottle comprising aninner layer or layers of an oxygen-scavenging composition and the innerlayer or layers being between outer layers of a structural polymer orpolymers and wherein the oxygen-scavenging performance as measured onthe aqueous liquid filled bottle is greater then the scavenging ratemeasured on the unfilled bottle.

One further aspect is a xylidene-substituted polyamide for use as anoxygen scavenger which has been treated under solid-stating conditionsand mixed with from 250 to 850 ppm of cobalt.

Another aspect is a transparent multilayer bottle for beer comprisingtwo inner layers of a xylidene-substituted polyamide and 250 to 850 ppmof cobalt, and a core layer and two outer layers of biaxially-orientedPET, where the thicknesses of each of the polyamide layers is in therange of 0.00254-0.0254 mm and each core and each outer layer is in therange of 0.0254 to 0.0508 mm, and the polyamide has been treated undersolid-stating conditions.

Yet another aspect is a container for enclosing an aqueous liquid, thecontainer having a wall comprising at least one layer of a solid-statedpolymer having a repeat unit containing a carbonyl, the polymercontaining at least 200 ppm of a transition metal.

Yet another aspect is a container for enclosing an aqueous liquid, thecontainer having a wall comprising at least one layer of a solid-statedpolymer having a repeat unit containing a carbonyl, wherein the wall hasa haze of less than 10%.

Yet another aspect is a container for enclosing an aqueous liquid, thecontainer having a wall comprising at least one layer of a polymerhaving a repeat unit containing a carbonyl, the polymer containing atleast 200 ppm of a transition metal, wherein the wall has a haze of lessthan 10%.

Yet another aspect is a container for enclosing an aqueous liquid, thecontainer having a wall comprising at least one layer of a solid-statedpolymer having a repeat unit containing a carbonyl, the polymercontaining at least 200 ppm of a transition metal, wherein the wall hasa haze of less than 10%.

These and other features of the present invention will be moreparticularly understood with regard to the following detaileddescription and drawings.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a side elevational view of a multi-layer preform incorporatingtwo layers of an enhanced scavenging polymer according to one embodimentof the present invention;

FIG. 2 is a side elevational view of a multi-layer container having atransparent sidewall made from the preform of FIG. 1;

FIG. 3 is a horizontal cross-section taken along line 3-3 of FIG. 2,showing the multi-layer sidewall of the container;

FIG. 4 is a vertical cross-section of a blow molding apparatus formaking the container of FIG. 3;

FIG. 5 is a graph of dissolved O₂ in a liquid in the container(ordinate) versus time in weeks (abscissa), for sample containers filledwith deoxygenated water and held at 72° F. (22° C.) and 50% relativehumidity, illustrating the oxygen-scavenging rate of various prior artcontainers compared to a container of the present invention;

FIG. 6 is an expanded portion of a graph similar to FIG. 5, showing aninitial 40 days, for comparing two sample containers of the presentinvention to other containers;

FIG. 7 is a graph similar to FIGS. 5 and 6 but showing an initial (14days) scavenging rate for removal of dissolved O₂ from a liquid in amulti-layer container of this invention which has been filled withoxygenated water (tap water);

FIGS. 8A and 8B are two graphs of percent transmittance (ordinate)versus wavenumbers in cm⁻¹ (abscissa) showing a substantial similarityin transmittance between MXD-6 which has not been solid-stated (8A), andenhanced MXD-6 which has been solid-stated for 60 hours (8B);

FIGS. 9A and 9B are two graphs of relative abundance (ordinate) versuswavelength converted to parts per million (ppm) (abscissa) for twosamples of MXD-6, one of which has not been solid-stated (9A) and theother of which has been solid-stated for 48 hours (9B);

FIG. 10 is a graph of GPC output of ultraviolet absorption at 254 nm(ordinate) versus time in minutes (abscissa) for a nonsolid-statedsample of MXD-6;

FIG. 11 is a graph of number average molecular weight Mn (ordinate)versus time of solid-stating in hours (abscissa) for an MXD-6 sample;

FIG. 12 is a graph of weight average molecular weight Mw (ordinate)versus solid-stating time in hours (abscissa) for an MXD-6 sample;

FIG. 13 is a graph of Z average molecular weight Mz (ordinate) versussolid-stating time in hours (abscissa) for a sample of MXD-6;

FIG. 14 is a graph of intrinsic viscosity (ordinate) versussolid-stating time in hours (abscissa) for various samples of MXD-6;

FIGS. 15A-15D are graphs of percent oxygen content (ordinate) versustime in days (ordinate) for various injection-molded plaque samples madefrom polyamide and cobalt, with and without solid-stating;

FIG. 16 shows a method of making an aromatic ester oxygen-scavengingpolymer from bisphenol A diacetate and adipic acid;

FIG. 17 is a bar graph of dissolved oxygen concentration after 9 weeks(ordinate) versus solid-stating time (abscissa) for containers includingenhanced polyamide and cobalt and filled with tank water;

FIG. 18 is a bar graph of a percent oxygen reduction (ordinate) after 54days by injection-molded plaque samples made from polyamide with variouscobalt concentrations, under dry conditions;

FIG. 19 is a bar graph of a percent oxygen reduction (ordinate) after 54days by injection-molded plaque samples made from polyamide with variouscobalt concentrations, under wet conditions;

FIG. 20 is a graph showing the effect of cobalt concentration on oxygencontent for 5-layer bottles made according to the present invention; and

FIGS. 21-22 are similar bar graphs to FIGS. 18-19.

DETAILED DESCRIPTION

The present invention relates in various aspects to enhancedoxygen-scavenging materials, a solid-stating process for enhancing theoxygen-scavenging rate of such materials, and plastic containers thatincorporate such materials whereby an actual reduction in the enclosedoxygen content is achieved.

With prior art glass containers, because glass is effectivelyimpermeable to oxygen, any oxygen ingress is believed to occur throughthe interface been the glass container and the lid or cap. The rate ofoxygen ingress due to cap leakage in a glass beverage container isbelieved to be about 2.1 ppb O₂ per day (see FIG. 5).

Because polymers that are completely impermeable to oxygen are largelyunknown, some oxygen will always enter a plastic container through thepolymer wall, causing an increase in the oxygen concentration within thecontainer over time. The rate of increase is related to the oxygenbarrier property of the polymer. In the prior art, improvements inperformance with either active or passive barrier polymers are reportedin terms of an overall increase in oxygen content over time.

According to a preferred embodiment, one advantageous feature of thepresent invention over prior art oxygen-scavenging materials is thatpackages made from the enhanced scavenger of the present invention areactually capable of removing oxygen from the inside of the packagefaster than external oxygen is allowed to enter the package. Thus,“oxygen-scavenging” as now defined herein refers to any process by whichoxygen is “removed” from an enclosed environment. For example,oxygen-scavenging results in a reduction of oxygen in a closed package.A material capable of oxygen-scavenging, i.e., an “oxygen-scavenger”,can remove oxygen from the defined environment chemically and/or byphysical absorption. Chemical removal of oxygen molecules can occur byoxidation of the scavenger (e.g., forming a chemical bond between atleast one oxygen atom of the oxygen molecule and a molecule of thescavenger). Physical removal of oxygen typically refers to a physicalabsorption by the scavenger, for example, where the oxygen molecules arephysically entrapped within the scavenger itself.

An “enclosed oxygen content” refers to an amount of oxygen present in asealed package, e.g., container. In some applications, e.g., for storingan oxygen-sensitive solid product, the relevant enclosed oxygen contentmay be the oxygen concentration of the atmosphere within the container.In other applications, e.g., where the container is used for storing aliquid, the relevant enclosed oxygen content may be the oxygenconcentration of the liquid. The oxygen enclosed within a container candepend on factors other than transmission through a plastic wall. Forexample, there can be leakage through the connection between the cap andbottle. Generally it is desirable to minimize any such leakage byselection of a specific bottle and cap pair. For example, an “Alcoaaluminum cap” having a non-reactive lining (i.e., compatible with thecomposition of the bottle) is widely used to minimize leakage of oxygeninto plastic containers (available from Silgan Containers Mfg. Corp.,1701 Williamsburg Pike, Richmond, Ind., USA, product R034831, linerEVA300, 28 mm rolled on pilfer-proof cap).

In one embodiment, a package is provided for an aqueous liquid product,the package having a wall including an oxygen-scavenging polymericcomposition such that an enclosed oxygen content is reduced. “Aqueousliquid” refers to any liquid having a substantial concentration ofwater. Examples of aqueous liquids include juice, tomato sauce, soysauce, and an alcoholic beverage that contains a significant portion ofwater, e.g., beer, wine or other liquor.

A “wall” comprises a single layer or multiple layers (multi-layer) andthe thickness of the wall is the thickness of the single layer or atotal thickness of the multiple layers. In one embodiment, the wallcomprises a multi-layer which includes at least one oxygen-scavenginglayer. Preferably each layer in the multi-layer comprises a polymer andthe multi-layer article is injection-molded. In a preferred embodiment,the oxygen-scavenging layer is an internal layer between exteriorstructural polymer layers. The structural layers provide mechanicalstrength and in preferred embodiments act as an “oxygen barrier” tolimit the transmission of oxygen through the container, at least fromthe exterior.

Exposing the oxygen-scavenging layer to air may cause degradation and/ordepletion of the oxygen-scavenger. By embedding the scavenger betweenoxygen-barrier layers, the barrier can serve to prevent a significantamount of oxygen from contacting the oxygen-scavenger, at least prior tofilling the container with the intended product. Once filled, interioroxygen can permeate through the inner structural layer(s) and be removedby the scavenger.

Solid-Stating Process

As used herein, “solid-stating” refers to a process where a polymer isexposed to heat under an atmosphere having a low oxygen content (i.e.,an oxygen content less than that of air) in order to enhance the oxygenremoval rate (hereinafter referred to as “oxygen scavengingperformance”) of the polymer. The solid-stating process shouldpreferably enhance the oxygen-scavenging performance of the polyamide bya factor of 1.3 for a given metal content and a given period of time.During solid stating, a low oxygen-content atmosphere can be provided byflushing the environment around the polymer with an inert gas, or bysubjecting the polymer to reduced pressure conditions (e.g., bysubjecting the polymer to a vacuum). Because the polymer is exposed toheat during the solid-stating process, the presence of excess oxygen maycause the polymer to undergo oxidation reactions. These oxidationreactions may result in thermal degradation of the polymer and thisdegradation may be observed as a discoloration of the polymer. Thus,performing the solid-stating process under a low oxygen-contentatmosphere can reduce the amount of polymer degradation by reducing theextent of oxidation. In addition, the polymer can be heated at a highertemperature when in a low oxygen-content atmosphere, which can provide agreater rate of enhancement of the oxygen-scavenging performance.Preferably, the low oxygen content environment is no greater than 10%oxygen.

In one embodiment, the solid-stating process involves heating thepolymer to a temperature greater than the glass transition temperatureof the polymer and less than the melting point temperature of thepolymer. Where the polymer is a crystalline aromatic polyamide (such asMXD-6), the solid-stating process involves heating the polyamide to atemperature from 150° C. to 210° C. In one embodiment, the uppertemperature for the solid-stating process is a temperature at which thepolymer begins to coagulate or form lumps. For example, it has beenfound that MXD-6 may coagulate at a temperature of 210° C. In anotherembodiment, the upper temperature for the solid-stating process is atemperature at which the polymer starts to decompose.

In one embodiment, the solid-stating process involves heating thepolymer in an inert gas such as argon or nitrogen. In anotherembodiment, the polymer can be heated under a vacuum comprising apressure of no greater than 15 torr, preferably a pressure of no greaterthan 10 torr, more preferably a pressure of no greater than 1 torr, andeven more preferably a pressure of no greater than 0.1 torr.

In one embodiment, the solid-stating process occurs over a time periodof at least 4 hours (h), preferably at least 8 h, more preferably atleast 24 h, and still more preferably at least 48 h.

Other processes can be used to treat the polymer in combination with thesolid-stating process. For example, prior to solid-stating, the polymercan be air dried or vacuum dried or both. Air drying typically involvesflushing the polymer with air. Vacuum drying involves subjecting thepolymer to a vacuum. The vacuum drying can be accompanied by a mildheating process where the polymer is heated to a temperature of lessthan the glass transition temperature. For example, a polyamide can bevacuum dried in a temperature range of 50° C. to 150° C.

It is understood that the solid-stating conditions can depend on acombination of factors such as temperature, time and a particularpressure to achieve a desired oxygen scavenging performance. Forexample, with a polymer such as MXD6, solid-stating at 0.1 torr for 6hours at 205° C. can provide a scavenger with moderately enhancedscavenger capabilities. Alternatively, moderately enhanced scavengingperformance can also be obtained by solid-stating MXD-6 at 0.1 torr for48 hours at 150° C. (a combination of lower temperature but longertime). Various factors such as cost, equipment, etc., may dictate whichparameters should be minimized (e.g., solid-stating time, temperature,or oxygen-scavenging performance) and accordingly, the appropriatesolid-stating parameters can be determined to achieve the desiredresults.

The solid-stating method can provide several advantages. In oneembodiment, solid-stating results in the polymer having a highercrystalline form. “Crystalline form,” as used herein refers to a statewhere substantial portions of the polymer have atoms arranged in aregular, ordered array, as understood by those of ordinary skill in theart. Typically, a polymer in a crystalline form has a higher meltingtemperature than an amorphous polymer, and this higher meltingtemperature allows the polymer to be solid-stated at a highertemperature, where higher temperature solid-stating processes canprovide an even greater enhancement of the oxygen-scavengingperformance. When the polymer is an amorphous polymer, the crystallineform can be induced prior to solid-stating by heating; thispre-solid-stating heating step may also be performed under a vacuum.

Other advantages of the solid-stating process may involve purifying theoxygen-scavenging polymer by removing volatile compounds, such as wateror organic compounds, that were initially present in the polymer.

The Metal

The enhanced oxygen-scavenging performance of certain polymers dependson the presence of a metal (although the metal need not be presentduring solid stating). The metal can be added in the form of the metalitself, as a salt or as a metal compound. In a preferred embodiment, theoxygen-scavenger comprises a polymer and a metal where the metal isadded as a metal compound. Metal compounds typically comprise twocomponents: a metal and a ligand which bonds to the metal and generallya substantial portion of the ligand is organic.

In one embodiment, the metal can be added to the polymer as a liquid, asolution mixture, in a crystalline form, as a pastille, or as a powderdepending on factors such as processing conditions. Typically, the metalis mixed with the polymer to create a physical blend. Theoxygen-scavenger, however, can eventually comprise a chemical bondbetween the metal and the scavenger or the ligand of the metal compoundand the scavenger where a chemical reaction occurs in the physical blendof the metal compound and the scavenging polymer. In other words, oncethe metal compound is processed with a polymer, the metal compound canbe present in the oxygen-scavenging polymer as the same initial metalcompound, a new metal compound, a salt or a metal atom. A new metalcompound can occur where at least a portion of the ligand no longerforms a chemical bond with the metal and a new ligand bonds to themetal. The new ligand can be the oxygen-scavenging polymer, or any othercomponents such as water, or any other organic component such as anorganic component that results as a by-product of scavenging polymerdegradation. Preferably, the initial metal compound is available in astable form, i.e., the metal compound is unreactive towards oxygenbefore addition of the compound to the oxygen-scavenging polymer.

The amount of metal present in the polymer is defined relative to theamount by weight in the polymer. It is understood that the desired metalconcentration can depend on a variety of factors or a combination ofthese factors such as molecular weight of the metal, molecular weight ofthe entire metal compound, polymer type or molecular weight of thepolymer. In one embodiment, the metal (e.g., cobalt) is present in anamount of at least 200 ppm based on the scavenging polymer, morepreferably from 200 ppm to 2000 ppm, even more preferably from 300 ppmto 1000 ppm, and still more preferably from 400 ppm to 800 ppm. Thelower limits of the metal concentration may be determined by a desiredlevel of oxygen-scavenging performance (i.e., insufficientconcentrations of metal may not achieve a desired scavenging performancefor a given application) and processability. The upper limit may bedetermined by factors such as cost, toxicity, transparency, color, orprocessability, depending on the particular application. See for examplethe plaque test results in Example 12 and the 5-layer bottle results inFIG. 20.

In one embodiment, the polymer is solid-stated in the presence of themetal. In another embodiment, the metal is added to (blended with) thesolid-stated polymer, after solid stating. Preferably, the metal isadded in a manner to prevent the incorporation of excess oxygen andwater to the solid-stated polymer. Thus, the metal in solid form (e.g.,powder, pellets, pastilles) can be dry tumbled in a sealed containerwith the solid-stated polymer. In one embodiment the metal is addedafter solid stating but in the same vessel used to solid-state thepolymer this reduces the opportunity for moisture to be added whenmixing the metal and polyamide. During a tumbling or agitation process,the solid-stated polymer and metal can be heated, and the heating stepcan be coupled with subjecting the polymer and metal to a vacuum. Thisheating step can facilitate uniform distribution of the metal about thepolymer, and further enhancements in scavenging performance. Thetemperature of this optional post solid-stating heating step is lessthan the temperature that would cause decomposition of the metal andpolymer and more preferably less than T_(g). For example, when combininga nylon (such as MXD-6) and cobalt, this temperature is no greater than130° C. and more preferably no greater than 70° C.

In one embodiment, the metal is a transition metal. The transition metalcan be selected from the group consisting of iron, cobalt, nickel,ruthenium, rhodium, palladium, osmium, iridium, platinum, copper,manganese and zinc. In a preferred embodiment, the metal is cobalt andmore preferably is added as a cobalt carboxylate compound. One exampleof a cobalt carboxylate compound is cobalt neodecanoate.

Performance Tests

One screening test (“the wet plaque test”) to determine an effectiveoxygen-scavenging composition of the present invention involvespreparing injection-molded plaques of the composition. Each plaque hasdimensions of 6.25 inches (158.75 mm) long by 1.75 inches (44.45 m) wideand having five equal sections with increasing stepped thicknesses of0.04 in (1 mm), 0.07 in (1.78 mm), 0.10 in (2.54 mm), 0.13 in (3.3 mm),0.16 in (4.06 mm). Seven plaques are enclosed in a 32-ounce glass jarand one ounce of water added under ambient air (21% oxygen at 23° C.).The plaques rest on a platform above the water in the jar. The jar iscapped with a standard canning jar lid, having a rubber septum. Asyringe is inserted through the septum to withdraw a gas sample from thejar; the gas sample is injected into a Mocon model PacCheck 450 HeadSpace Analyzer to measure the oxygen content (available from MoconModern Controls, 7500 Boone Ave North, Minneapolis, Minn. 55428 USA).After measuring an initial oxygen content (typically 21.3%), subsequentmeasurements should be taken over a period of several weeks. Effectiveoxygen scavengers will reduce the oxygen concentration in the jar to 19%or less within 54 days (see Table 6B).

Another screening test for effective oxygen-scavenging performance asencompassed by the present invention involves the same wet plaque testdescribed above, but the results are analyzed in terms of slopes. Agraph of measured oxygen content vs. time is prepared. The slopes ofthese plots provide an index (slope) to compare relative rates ofoxygen-scavenging. For example, when a solid-stated oxygen-scavengerexhibits an enhanced oxygen-scavenging performance over itsnon-solid-stated counterpart, its slope is at least 1.3 times greaterthan that of the non-solid-stated counterpart.

The enhanced oxygen-scavenging performance may alternatively bedetermined in select embodiments by finding an oxygen-scavengingperformance for a solid-stated polymer with a given metal content thatis greater than that of the corresponding non-solid-stated polymer/metalby a factor of at least 1.3, preferably by a factor of at least 2, andmore preferably 4 times or more.

Package Storage and Shelf Life

It is a surprising feature that certain oxygen-scavenging articles ofthe present invention are capable of being stored in the presence of anexcess of oxygen, such as air, for a significant period of time (e.g., 3months, preferably 6 months) without substantial loss of scavengingperformance when thereafter filled with a product. Thus, another aspectof the present invention provides a multi-layer package that issubstantially free of degradation under ambient conditions for a time ofat least three months. “Substantially free of degradation” refers to apackage that maintains a designated scavenging performance (when filled)to reduce the oxygen content within a defined environment, such as theoxygen content enclosed within the package. Degradative effects canarise from oxidative or other unwanted processes. In one embodiment, themulti-layer package has at least one oxygen-scavenging layer embeddedwithin two biaxially-oriented structural polymer layers, an arrangementwhich helps withstand degradative effects. The package is capable ofbeing stored under ambient conditions and being substantially free ofdegradation within a time of at least three months and more preferablyat least six months. “Ambient conditions” refers to an atmosphere of 21%oxygen (air) and a relative humidity of 50% at 23° C.

Another aspect of the present invention provides a package for enclosingan aqueous liquid that provides the package with an enhancedoxygen-removal rate upon being filled with the liquid. While not wishingto be bound by any theory, it appears that a component of the aqueousliquid is capable of activating the enhanced oxygen-scavengingperformance of the scavenging layer. This non-limiting theory mayreconcile two seemingly contradictory events: that a packageincorporating an oxygen-scavenging layer can be stored for at leastthree months in air while being substantially free of degradation, andyet upon being filled with an aqueous liquid, exhibit scavengingactivity. In one embodiment, the package enclosing the aqueous liquidhas an oxygen-removal rate greater than an oxygen-removal rate of a drypackage (see FIGS. 18-19).

In one embodiment, a structural layer is positioned between theoxygen-scavenging layer and the liquid; the structural layer ispermeable to a component of the aqueous liquid, allowing the aqueousliquid to activate the oxygen-scavenger.

In another embodiment, the present invention provides a compositioncomprising an oxygen-scavenging layer positioned adjacent a polymericstructural layer, the structural layer being water-saturated.“Water-saturated” refers to a polymeric composition that is permeable towater upon contact with a source of water, such as an aqueous beverage.

In one embodiment, the component of the aqueous liquid capable ofenhancing oxygen-scavenging performance is selected from the groupconsisting of water, carbon dioxide, nitrogen, volatile organiccompounds, low molecular weight oligomers and trace impurities. In apreferred embodiment, the component is water.

Layer Compatibility

According to another feature of the invention, the solid-stating methodprovides an enhanced oxygen-scavenging polymer that can be processed toform a variety of multi-layer articles. One indication of processabilityis intrinsic viscosity, which in turn affects melt viscosity (anotherprocess parameter). Intrinsic viscosity (IV) reflects the molecularweight and may reflect the shape of the polymer molecule itself. Forexample, rod-shaped polymer molecules have a different intrinsicviscosity than spherical molecules for molecules of the same molecularweight, as is well-known in the art.

Intrinsic viscosity can be determined from inherent viscositymeasurements for resins, such as polyester resins. For example, applyingthe procedure of ASTM D-4603-91, and employing PET soluble at 0.50%concentration in a 60/40 phenol/1,1,2,3-tetrachloroethane solution at30° C., the inherent viscosity data can be determined and then convertedto intrinsic viscosity using the Billmeyer relationship (see ASTM4603-91, section 11). Polyethylene terephthalate (PET) having anintrinsic viscosity of about 0.8 is widely used in the carbonated softdrink (CSD) industry. Polyester resins for various applications mayrange from about 0.55 to about 1.04, and more particularly from about0.65 to 0.85 dl/g. As used herein PET is meant to include PEThomopolymers and copolymers.

A conventional parameter for processability is melt viscosity, asindicated by a melt index. “Melt index” can generally be defined as anumber of grams of polymer that can be forced through an orifice of astandard unit at a specified temperature and pressure over a definedperiod of time. The melt index can be measured according to ASTM MethodD-1238-94a. For example, using a 2.16 kg load and at 215° C., Shell 8006virgin PET has a melt index of 29 g/10 minutes (available from ShellChemical Co., Houston, Tex.). The polymers as used herein(oxygen-scavenging polymers and biaxially-oriented polyester polymers)are high molecular weight polymers, having a molecular weight of atleast about 45,000, for which the melt viscosity is an important processparameter. If the melt viscosity is too high, it is not possible to pushthe polymer through an injection manifold fast enough to producecommercially acceptable preforms. Another important parameter reflectedby melt index is melt strength; if the melt strength is too low, it isnot possible to maintain layer integrity in a multi-layer structurehaving one or more relatively thin layers. Generally, as the molecularweight of the polymer increases, both the melt viscosity and meltstrength increase. For multi-layer applications, those skilled in theart can determine an appropriate combination of melt viscosity and meltstrength for a scavenging polymer layer positioned adjacent layers ofother polymer-types.

In the situation where a structural layer is positioned adjacent anoxygen-scavenging layer in the absence of an adhesive, it is preferablethat the two layers be “compatible.” Compatibility implies that themulti-layer article, having at least two layers positioned adjacent eachother, have the structural integrity to withstand delamination,observable deformation from a desired shape, or any kind of degradationof a layer caused by a chemical or other process initiated by anadjacent layer during, the article-forming process or in the finalproduct during expected use. Compatibility can be enhanced by selectingintrinsic viscosities, melt viscosities, melt indices and solubilityparameters that allow one of ordinary skill in the art to achievedesired bottle characteristics. If a recyclable bottle is desired, thenthe layers should readily separate when the bottle is cut to enableseparate processing of the different materials.

For a multi-layer article incorporating an oxygen-scavenger and astructural polymer, it is preferred that the melt index of thescavenger, e.g., polyamide, is less than that of the structural polymer,e.g., PET. The melt index of the scavenger should also take into accountthe increase in melt index that can occur for example when a metal(e.g., cobalt) is added. Thus, one aspect of the present inventionprovides a method for adjusting a melt index of a polymer such as apolyamide, by adding a metal to the polyamide in a specified amount toachieve a polyamide having an increased melt index. The method presentsan advantageous feature of adjusting a melt index of the polyamide toallow it to be compatible with other polymers especially in amulti-layer article. In one embodiment, the metal is cobalt.

In one example, the melt index of PET going into the injection mold is30 g/10 min. and the melt index of MXD-6 with cobalt is 20 g/10 min.Before the addition of cobalt, the melt index of the MXD-6 is 10 g/10min. The melt index of the scavenger can increase further in theinjection molding machine. The extent of this increase depends onfactors that may vary for different injection mold units, such as theresidence time of the scavenger in the injection mold and thetemperature that the scavenger is subjected to in the injection mold. Inone embodiment, a polyamide oxygen-scavenging polymer has a melt indexof from 10 g/10 min. to 15 g/10 min before the addition of cobalt, whenused with adjacent PET layers.

It is further noted that solid-stating can provide enhanced-oxygenscavenging independent of any substantial increase in intrinsicviscosity. As discussed in greater detail in Example 10 below, aninitially large increase in oxygen-scavenging performance can beobserved within the initial 8 h of the oxygen-scavenger being exposed tothe solid-stating process. During this time interval, the increase in IVis relatively small compared to the improvement in oxygen-scavengingperformance.

In one embodiment, the solid-stating process causes an increase inintrinsic viscosity of the scavenging polymer. For use in a sequentialinjection molding process with adjacent layers of PET, the scavengingpolymer can be a polyamide such as MXD-6; the polyamide shouldpreferably have an intrinsic viscosity from 1.7 to 2.0, more preferablyfrom 1.73 to 2.0, more preferably still from 1.75 to 1.9, and even morepreferably still from 1.80 to 1.86; all of these values are obtainedwhen the intrinsic viscosity measurements are performed with m-cresolsolvent. These desired IV values for MXD-6 are before the addition ofthe metal.

When a metal such as cobalt is added to the solid-stated polymer, the IVmay be reduced. A skilled person can select a desired IV range for theparticular scavenger (polymer and metal) when injected or extruded withadjacent layers of particular structural polymers.

In addition to a match of IV, the process compatibility of thescavenging polymer and an adjacent polymer can further be indicated bythe respective glass transition temperatures (T_(g)) of the twopolymer-types, whereby the polymers can be processed in the sametemperature range without loss of transparency. Solubility parameterscan provide another factor in considering compatibility.

Transparency

Another advantageous feature of the oxygen-scavenging package of thepresent invention is transparency. In one embodiment, only a portion ofa package need be transparent. For example, in a beverage container thecontainer should at least have a transparent sidewall because typicallya consumer views the contents of the bottle through the sidewall (asopposed to the base or the neck finish). Of course, completelytransparent bottles including a transparent base and neck finish arealso encompassed by the present invention.

In some applications, the package may include coloring dyes which reducethe transparency. As used herein, a “transparent” wall or article refersto the wall or article without dyes.

As used herein transparency is determined by the percent haze fortransmitted light through the wall (H_(T)) which is given by thefollowing formula:H _(T) =[Y _(d)÷(Y _(d) +Y _(s))]×100where Y_(d) is the diffuse light transmitted by the thickness of thespecimen, and Y_(s) is the specular light transmitted by the thicknessof the specimen. The diffuse and specular light transmission values aremeasured in accordance with ASTM Method D 1003, using any standard colordifference meter such as model D25D3P manufactured by Hunterlab, Inc.,Reston, Va., U.S.A. In one embodiment, at least a portion of the packageand preferably at least the sidewall should have a percent haze (throughthe wall) of no greater than 10%, more preferably no greater than 7% andmore preferably still, no greater than 5%.Scavenging Polymers

A preferred class of oxygen-scavenging polymers is defined as a polymerhaving a repeat unit including a carbonyl. The repeat unit of theoxygen-scavenging polymer can also include aromatic or aliphatic groupsin the polymer backbone or a side chain; “backbone” is defined as thelongest, continuous bond pathway in the polymer. The repeat unitpreferably as at least one hydrogen atom alpha to the carbonyl. Theoxygen-scavenging polymer can be homopolymer, a random copolymer, analternating copolymer, a block copolymer, or a lend. Preferably, thescavenging polymer will form a transparent layer. The scavenger mayinclude other functional groups as long as the compatibility with otherpolymers is maintained when the oxygen-scavenging polymer isincorporated in a multi-layer article.

In one embodiment, the oxygen-scavenging polymer has a repeat unitincluding an amide group, also known as a polyamide. An amide is definedas having a unit —RN—C(O)— where R can be hydrogen, alkyl or aryl. In apreferred embodiment, the polyamide is a nylon where the backboneincludes aromatic and/or aliphatic groups. Examples include MXD-6, nylon6, or nylon 6,6. In one preferred embodiment, the backbone includesaromatic groups derived from xylidene monomers which include m-xylidene,i.e., MXD-polyamides. One example of an MXD-polyamide can be formed bypolymerizing meta-xylylene-diamine (H₂NCH₂-m-C₆H₄—CH₂NH₂) with adipicacid (HO₂C(CH₂)₄CO₂H), to produce the polymer MXD-6 (sold by MitsubishiChemicals, Japan). Another example of an aromatic polyamide is obtainedby the polymerization of meta-xylilene-diamine and adipic acid (same asMXD-6) but with the addition of 11 mole percent isophthalic acid (C₆H₄—(COOH)₂). This polymer is sold by EMS of Domat/EMS, Switzerland. Anexample of an aliphatic polyamide is nylon-6 (PA 6)(see FIG. 15D).Typically, amorphous polyamides have a T_(g) of from 90° C. and 150° C.

In one embodiment, the oxygen-scavenging polymer is a polyester. Apreferred aromatic ester scavenging polymer is described incommonly-owned and copending PCT Application No. US97/16826 filed Sep.24, 1997, entitled “Transparent Oxygen-scavenging Article IncludingBiaxially-Oriented Polyester, And Method Of Making The Same,” publishedon Apr. 2, 1998 as WO 98/13266 (docket no. C0762/7217WO), which ishereby incorporated by reference in its entirety.

In one embodiment, the oxygen-scavenging polymer is a polyketone, alsoreferred to as poly(olefin-ketones), which are linear, alternatingcopolymers having a repeat unit including the group:

where R¹-R³ can be the same or different and each can be selected fromthe group consisting of hydrogen, an organic side chain, or asilicon-containing side chain. The simplest member of this class ofpolyketones is the alternating copolymer of ethylene and carbon monoxide(E/CO). It is possible to introduce a second olefinic monomer into thepolymerization, such as propylene, which will substitute randomly forethylene, and in alternation with carbon monoxide, to produce theterpolymer poly(ethylene-alt-carbon monoxide)-stat-(propylene-alt-carbonmonoxide) (hereinafter E/P/CO terpolymer).Structural Polymers

Generally, at least one other layer will function as a structuralpolymer layer in the situation where the oxygen-scavenging layer byitself cannot maintain the desired structural integrity of the article.Desirable features of structural polymers include any one or acombination of the following: unreactive towards oxygen, water or anyorganic component; suitable for contact with food; permeable to oxygenunder select conditions; functional as a passive barrier layer toprevent a substantial amount of oxygen from the outer environment(outside of the package) reaching the oxygen-scavenging layer. In oneembodiment, the structural polymer is selected from the group consistingof polyesters and polyolefins. In a preferred embodiment, the structuralpolymer is an aromatic polyester. An important feature of the structuralpolymer is biaxial orientation which in addition to improving themechanical strength may also improve the oxygen barrier property. In oneembodiment, the structural polymer is PET and is biaxially stretched(for example in a bottle sidewall) at a planar stretch ratio of from 7×to 14×, preferably from 8× to 12×. The ability to affect permeabilityproperties through biaxial orientation may have an effect on the overallscavenging performance of a multi-layer article where the structurallayers form outer and inner exterior layers and the scavenging layer isan interior layer, i.e., the overall performance is based on the rate ofoxygen removal from the interior of the container (where oxygen canpermeate the inner structural layer to reach the scavenging layer andwhere the rate of removal exceeds a rate at which exterior oxygen canpermeate to the interior of the package).

Generally, the glass transition temperature T_(g) of a polyester used ina commercial plastic container is at least 5° C. above the ambient usetemperature, e.g., if a beverage bottle will be used in an environmentwhere the temperature may reach 35° C., the polymer should have a T_(g)of at least 40° C. or the polymer may melt (no longer be a solidarticle). The T_(g) also determines the temperature above which anaromatic polyester can be heated to enable biaxial stretching. Forexample, PET has a T_(g) of 70° C., and PEN has a T_(g) of 120° C. Forease of processing, the polymers are typically stretched in anorientation temperature range at least 20° C. above T_(g) (e.g., atleast 90° C. for PET, at least 140° C. for PEN, and varying with thecopolymer content). It may be desirable for the scavenging polymer tohave a T_(g) below the orientation temperature of the polyester which isto be biaxially oriented (e.g., PET or PEN), but not so far below thatthe scavenging polymer will crystallize (become nontransparent oropaque) during the orientation process. In such case the T_(g) of thescavenging polymer would be at least 10° C. below the orientationtemperature used to biaxially orient the polyester. A preferred range ofT_(g) for a scavenging polymer having an amorphous nature (i.e., notcrystallizing more than 3% under any conditions) is 0-15° C. below theT_(g) of the polyester, more preferably 3-7° C. below, and mostpreferably 5° C. below. A preferred range of T_(g) for a crystallizablescavenging polymer is 0-15° C. above the T_(g) of the polyester, morepreferably 3-7° C. above, and most preferably about 5° C. above.Relative ratios of monomers in a copolymer can be varied to adjust theT_(g) of the scavenging polymer. In one embodiment, increasing thearomatic groups in the backbone of a polyester scavenging or structuralpolymer will increase the T_(g); a desired T_(g) enables biaxialorientation of adjacent polyester layers while maintaining transparencyof the overall article.

Packages and Multi-Layer Articles

Packages of the present invention include articles for storing food orother products; the package can be a blow-molded container, aninjection-molded container, and a film (e.g., for wrapping meat,vegetable, fruit). The intended application will dictate the desiredpackage characteristics; for example, a film for wrapping food will nothave the same rigidity requirements as a plastic bottle. However, thefilm thickness may be greater than typical (for nonscavengingapplications) in order to provide the desired scavenging performance.

The thicknesses of the oxygen-scavenging and structural layers willgenerally effect the oxygen-scavenging performance of the package.Generally, multi-layer articles having thicker scavenging layers resultin a better scavenging performance. Other factors however, may providean upper limit to scavenging layer thickness. For example, in commercialapplications it is generally desired that the cost of theoxygen-scavenging layer be minimized. The cost of incorporating apolyamide into a multi-layer container can be significant compared to acontainer made solely of polyethylene terephthalate. The methods andarticles of the present invention can be used to achieve a costreduction by, for example, providing one or more relatively thinscavenging layers (compared to the overall thickness of the article). Inone embodiment, by using separate oxygen-scavenging layers as opposed toblends (of the scavenger and other polymers), thinner oxygen-scavenginglayers may be used with thicker structural layers and subsequently costis minimized while processing conditions and/or final bottlecharacteristics are optimized. Where the oxygen-scavenging layerincludes a metal, a relatively high concentration of metal can beincorporated in the separate layer. In contrast, a blend will typicallyhave a lower concentration of metal spread over a thicker layer (buthave a higher metal concentration in the overall package).

It has been found that for some applications, optimizing the amount ofmetal and oxygen-scavenging polymer in a relatively thinner portion ofan article optimizes the oxygen-scavenging performance. For example,when two thin intermediate layers of an oxygen-scavenging polymer areincorporated in a 5-layer injection molded preform for making a bottle,as described hereinafter, where the scavenging layers comprise asolid-stated polyamide and cobalt, if the amount of cobalt is greaterthan 1000 ppm (based on the polyamide weight) and/or the weight of thescavenging polymer in the preform is no greater than 10% by weight, itmay be difficult to provide a desired concentration of cobalt and/oramount of oxygen-scavenging polymer in the relatively thin sidewallportion of the container. One reason for this is that cobalt willdecrease the IV of the polyamide, thereby affecting the materialdistribution of the layers during injection. Thus, depending on thescavenger used, the composition of adjacent layers, the thicknesses ofthe various layers, and the processing technique (simultaneous injectionmolding, sequential injection molding, extrusion, film-forming, etc.),there may be upper and/or lower limits on the amount of metal used whileattempting to achieve a desired oxygen-scavenging performance.

In general, the thicknesses of the scavenging/structural layers arepreferably selected to allow the bottle to have a substantial storageperiod unfilled and a reasonable rate of removal of oxygen from thepackage when filled, both factors being tailored to the particular foodproduct being stored. The outer layers should be thick enough to preventoxygen permeating to the scavenging layer in an amount in excess of thatwhich can be removed by the scavenger. The thickness of the innerstructural layer (i.e. the layer closest to the food product) must alsobe thin enough to allow the enclosed oxygen content, often having a lowpartial pressure of oxygen, to permeate the inner layer at acommercially acceptable rate allowing for reduction of the oxygencontent. The more active the oxygen scavenger, the less thicknessrequired of the structural layer. As mentioned previously, structurallayers that are too thin may reduce the storage period to unacceptablelevels.

In one embodiment, the thickness of the outer and inner structurallayers are the same. This arrangement optimizes the balance betweenstorage period and scavenging rate. In addition, the structural layersare preferably permeable to a component of an aqueous liquid when thepackage is filled and this component is capable of enhancing thescavenging rate of the scavenging layer and/or rate of permeation ofoxygen through the inner structural layer.

In a preferred embodiment described below, the multi-layer article canbe used as a package, where the package contains a product that requiresstorage under low oxygen conditions. For example, the product can be afood or beverage (e.g., beer, juice, ketchup) and the multi-layerarticle can be a bottle having an opening that can be sealed with astandard cap. The product can include a pressurized liquid, e.g., bycarbon dioxide or nitrogen, wherein the container maintains the productpressure and maintains a low oxygen content.

Typically, a multi-layer container such as a bottle is a blow-moldedarticle made from an injection-molded multi-layer preform. The preformmay comprise a neck finish, a sidewall-forming portion and abase-forming portion. The multiple layers of the preform can be formedby any method known in the art. In one embodiment, the multi-layerpreform can be formed by applying or injecting various materialsindividually (sequentially) into a mold. In another embodiment, themulti-layer preform can be formed by simultaneous injection of thedesired layers into the mold. In another embodiment, where the containeris a film for wrapping food, the multi-layer can be formed byco-extruding multi-layer sheets. Certain techniques encompassed by atleast some of these various embodiments for forming multi-layer articlesare described in U.S. Pat. No. 5,281,360 (Hong et al.), which is herebyincorporated by reference in its entirety.

In a preferred embodiment, the preform has a particular multi-layerarrangement such that when the preform is formed into a bottle, asignificant portion of the oxygen-scavenging layer is contained in thethinnest portion of the bottle, namely the sidewall. In someapplications, substantially the entire container body (below the neckfinish) includes a layer of the oxygen-scavenging polymer. As previouslydiscussed, it has been found that the choice of polymers and polymerprocessing conditions can affect the location of a significant portionof the oxygen-scavenging layer.

In a preferred 5-layer embodiment, the bottle has two intermediateoxygen-scavenging layers (polyamide/cobalt) positioned between inner,core, and outer structural polymer layers (PET)—see e.g., the 5-layerbottle of FIGS. 1-4 described below. Typically, the neck finish and/orbase of the container will have a thicker structural layer. Where aportion of the container has a thicker structural layer, a lesserthickness of the scavenger layer (than in the other bottle portions) mayprove to be adequate. In the 5-layer embodiment, the oxygen-scavengingpolymer/layer is preferably no greater than 15% by weight of the bottle,while providing sufficient scavenger in the sidewall for a desiredperformance. Preferably, from a cost perspective, the weight percentageof the scavenger is no greater than 10%, e.g., 5-8%. In someapplications, the scavenger could be 2-5% by weight.

Surprisingly, it has been found that for storage purposes, it ispreferable to store the multi-layer article as a bottle, rather than apreform. In contrast, many prior art teachings recommend storing thearticle as a preform, and then blow-molding the bottle immediately priorto use (filling). For example, bottles of this invention stored(unfilled) for up to 233 days still maintain excellent scavengingproperties when filled with an aqueous liquid, whereas the scavengingperformance decreases when preforms of this invention have been storedfor a comparable amount of time. While not wishing to be bound by anytheory, it is believed that the preform versus bottle effect may arisefrom the biaxial orientation of the PET structural layers in the bottlewhich reduces the oxygen permeability.

In a 5-layer beverage bottle application as described herein, athickness of each of two oxygen-scavenging layers in thesidewall-forming portion of the preform is preferably from 0.001 to 0.01in. (0.0254 mm to 0.254 mm), and more preferably from 0.004 to 0.005 in.(0.102 mm to 0.127 mm). A total thickness of the preform is preferablyfrom 0.1 to 0.3 in. (2.54 mm to 5.08 mm), and more preferably from 0.14to 0.17 in. (3.56 mm to 4.32 mm). The thickness of each structuralpolymer layer (inner, core, outer) is preferably from 0.01 to 0.1 in.(0.254 mm to 2.54 mm), and more preferably from 0.03 to 0.08 in. (0.762mm to 2.03 mm). Alternatively, the two scavenger layers may be combinedinto a single scavenger layer in the sidewall (at double the thicknessof one scavenger layer).

The resulting bottles (of the 5-layer embodiment) preferably have anaverage sidewall thickness from 0.01 to 0.02 in. (0.254 mm to 0.508 mm).Each of the two oxygen-scavenging layers in the sidewall has a thicknessof preferably from 0.0001 to 0.001 in. (0.00254 mm to 0.0254 mm), andmore preferably from 0.0004 to 0.0006 in. (0.0102 mm to 0.0152 mm). Eachstructural polymer layer (inner, core, outer) in the sidewall preferablyhas a thickness of from 0.001 to 0.02 in. (0.0254 mm to 0.0508 mm), andmore preferably from 0.003 to 0.008 in. (0.0762 mm to 0.203 mm). Again,as an alternative, the two separate scavenger layers can be combinedinto one (at double the thickness).

The scavenging performance of this bottle can be determined by a methodwhich involves filling the bottle with a volume of a liquid (e.g.,water), sealing the bottle, storing the liquid in the bottle for aperiod of time and monitoring the oxygen content to ascertain theamount/rate by which the oxygen content is reduced in the liquid duringthe storing (see Example 6). By reason of the enhanced scavengingperformance of the present invention, there will be a reduction in theoxygen content of the liquid in the plastic bottle. For the purpose ofthis test it may take some short time (in hours or one or two days) forthe reduction to be measurable; this would still be considered a casewhere the oxygen scavenging occurs immediately upon filling. The timedelay for a measurable reduction may be due to the equipment ormeasuring process. Preferably, the reduction from the initial oxygenlevel is sustainable for 16 weeks. In contrast, there is an overall gainin oxygen content in a glass bottle.

By reducing the oxygen content of the package, it can be seen that theshelf life of the product can be increased considerably. A desiredreduction of oxygen content (for the desired shelf life) can be effectedby for example selecting an appropriate metal concentration in theoxygen-scavenging layer. For example, where the oxygen-scavenging layercomprises a polyamide such as MXD-6 and cobalt, it has been found that acobalt concentration of at least 200 ppm can achieve this reduction ofoxygen in the liquid in the 5-layer embodiment.

For example, when a 500 ml commercial beer bottle is filled with beer(3% headspace), the oxygen content of the beer is typically around 100ppb. In a multi-layer container of the present invention, this initialoxygen content (100 ppb) can be reduced such that the oxygen content isless than 100 ppb over some extended period of time, more preferably nogreater than 50 ppb, and still more preferably no greater than 25 ppb.In one embodiment, the oxygen reducing performance is such that theoxygen content is held at no greater than 25 ppb from the time period ofabout one week (after fiiling) and for the following 16 weeks (see FIG.5).

The method for reducing oxygen content can involve a component of theliquid, such as water, permeating into one or more of the structural andoxygen-scavenging layers. This component may promote transmission ofoxygen to the scavenger layer and thus enhance the scavengingperformance. In the 5-layer embodiment, the two oxygen-scavenging layersare positioned between three structural polymer layers where onestructural layer is an inner layer that is in contact with the liquid, asecond structural layer is a core layer having opposing sides positionedadjacent the two oxygen-scavenging layers, and a third structural layeris an outer layer in contact with air. In this embodiment, the liquidcan permeate the inner structural polymer layer and consequently,permeate the oxygen-scavenging layer whereby the component of the liquidcan help initiate or enhance the oxygen-scavenging. The component can beselected from the group consisting of one or more of water, carbondioxide, nitrogen, volatile organic compounds, low molecular weightoligomers and trace impurities. The outer polymer layer, which willtypically be in contact with the outside environment or air, may not beexposed to this component (from the liquid) that activates theoxygen-scavenging layer, at least not to the same degree. By thismethod, the outer layer(s) can prevent inward oxygen transmission whilethe inner scavenger layer(s) of the bottle can be activated to reactwith oxygen from inside the container. Furthermore, prior to filling,the bottle can be stored for long periods without consuming thescavenger (i.e., when the component is not present).

Thus, the action of filling the container with a liquid can allow theliquid (or a component thereof) to permeate the structural and scavengerlayers and provide immediate scavenging. This eliminates the agingrequirement noted for certain prior art containers. Thus, the bottlescan be stored dry, while preserving their ability for immediatescavenging when filled.

Enhanced Scavenging/Beer Bottle

FIGS. 1-4 illustrate a transparent 5-layer preform and beer containerincluding two solid-stated oxygen-scavenging polymer layers according tothe present invention. This multi-layer structure enables use of arelatively low-weight percentage of the scavenging polymer, e.g., about7½ percent of the total container weight, while providing a high levelof scavenging.

An injection-molded multi-layer preform 30 is shown in FIG. 1. Thepreform is substantially cylindrical, as defined by vertical centerline32, and includes an upper neck portion or finish 34 integral with alower body-forming portion 36. The neck portion has a top sealingsurface 31 which defines an open top end of the preform, and a generallycylindrical exterior surface with threads 33 and a lowermost flange 35,Below the flange is the body-forming portion 36 which includes an uppercylindrical portion 41, a flared shoulder-forming portion 37 whichincreases radially inwardly in wall thickness from top to bottom, acylindrical panel-forming section 38 having a substantially uniform wallthickness, and a substantially hemispherical base-forming section 39.

Preform 30 has a three-material, five-layer (3M, 5 L) structure (notshown in FIG. 1) and is substantially amorphous and transparent. Themultiple preform layers comprise, in serial order: an outer layer ofvirgin PET, an outer intermediate layer of a solid-statedoxygen-scavenging polymer, a central core layer of recycled PET, aninner intermediate layer of a solid-stated oxygen-scavenging polymer,and an inner layer of virgin PET. The virgin PET may be any commerciallyavailable, bottle-grade PET homopolymer or copolymer having an intrinsicviscosity (IV) of about 0.80 dl/g. The core layer is commerciallyavailable post-consumer PET having an IV of 0.73 dl/g. The twointermediate layers are made of solid-stated MXD-6 scavenging polymer aspreviously described, having an intrinsic viscosity for example of 1.27dl/g, a T_(g) of 87° C., and a melting point of 238° C. The scavengingpolymer includes 500 micrograms of cobalt per gram of polymer (i.e., 500ppm cobalt per weight of MXD-6); the cobalt is added as cobaltneodecanoate.

The preform 30 is adapted for making a 0.5 liter (500 ml) pressurizedcontainer for beer, as shown in FIG. 2. The preform 30 has a height ofabout 112 mm, and an outer diameter in the panel-forming section 38 ofabout 25 mm. The total wall thickness of the panel-forming section 38 isabout 4 mm; the thickness of the various layers in this preform sectionare: outer and inner layers each about 1.1 mm thick; inner and outerintermediate layers each about 0.11 mm thick; and core layer about 1.6mm thick. For carbonated beverage containers of about 0.3 to 1.5 litersin volume, having a panel wall thickness of about 0.25 to about 0.38 mm,and filled at about 2.0 to 4.0 volumes of CO₂ aqueous solution, thepreform panel-forming section 38 preferably undergoes an average planarstretch ratio of about 9-12. The planar stretch ratio is the ratio ofthe average thickness of the preform panel-forming portion 38 to theaverage thickness of the container panel 46 (as shown in FIG. 2); theaverage is taken along the length of the respective preform andcontainer portions. The average panel hoop-stretch is preferably about4.0 to 4.5, and the average panel axial stretch is about 2 to 3. Thisproduces a container panel 46 with the desired biaxial orientation andvisual transparency. The specific panel thickness and stretch ratioselected depend on the dimensions of the bottle, the internal pressure,and the processing characteristics (as determined for example by theintrinsic viscosity of the particular materials employed).

The preform shown in FIG. 1 may be injection molded by a sequentialmetered process described in U.S. Pat. Nos. 4,550,043; 4,609,516;4,710,118; 4,781,954; 4,990,301; 5,049,345; 5,098,274; and 5,582,788,owned by Continental PET Technologies, Inc. of Florence, Ky., and herebyincorporated by reference in their entirety. In this process,predetermined amounts of the various materials are introduced into thegate of the preform mold as follows: a first shot of virgin PET whichforms partially-solidified inner and outer preform layers as it moves upthe cool outer mold and core walls; a second shot of the scavengingpolymer which will form the inner and outer intermediate layers; and athird shot of the recycled PET material which pushes the scavengingpolymer up the sidewall (to form thin scavenging layers) while the thirdslot forms a central core layer. A final shot of virgin PET may be usedto clear the nozzle and finish the bottom of the preform with virginPET.

After the mold is filled, the pressure is increased to pack the moldagainst shrinkage of the preform. After packing, the mold pressure ispartially reduced and held while the preform cools. In a standardprocess, each of the polymer melts are injected into the mold at a rateof about 10-12 grams per second; a packing pressure of about 7500 psi(50×10⁶ N·m⁻²) is applied for about 4 seconds after filling; thepressure is then dropped to about 4500 psi (30×10⁶ N·m⁻²) and held forthe next 15 seconds, after which the pressure is released and thepreform is ejected from the mold. Increasing the pressure above theselevels may force higher levels of interlayer bonding, which may includechain entanglement, hydrogen bonding, low-level interlayercrystallization and layer penetration; these may be useful in particularapplications to increase the resistance to layer separation in both thepreform and container. In addition, increased pressure holds the preformagainst the cold mold walls to solidify the preform without haze, i.e.,loss of transparency, at the minimum possible cycle time. Still further,faster injection rates may yield higher melt temperatures within theinjection cavity, resulting in increased polymer mobility which improvesmigration and entanglement during the enhanced pressure portion of theinjection cycle, and thus increases the delamination resistance. As anadditional option, increasing the average preform temperature and/ordecreasing the temperature gradient through the preform wall may furtherreduce layer separation by minimizing shear at the layer boundariesduring preform expansion.

FIG. 4 illustrates a stretch blow-molding apparatus 70 for making thecontainer 40 from the preform 30. More specifically, the substantiallyamorphous and transparent preform body-forming section 36 is reheated toa temperature above the glass transition temperatures (T_(g) of theinner/outer virgin PET, intermediate scavenger, and core recycled PETlayers, and the heated preform then positioned in a blow mold 71. Astretch rod 72 axially elongates (stretches) the preform within the blowmold to insure complete axial elongation and centering of the preform. Ablowing gas (shown by arrows 73) is introduced to radially inflate thepreform to match the configuration of an inner molding surface 74 of theblow mold. The formed container remains substantially transparent buthas undergone strain-induced biaxial orientation to provide theincreased strength necessary to withstand the carbonation pressure.

In this embodiment the preforms are reheat stretch blow-molded on aSidel SBO-1 into 500 ml beer bottles with an average sidewall thicknessof 0.015 in. In the sidewall, the inner PET layer is 0.0037 in. thick,the inner intermediate layer is 0.0005 in., the core layer is 0.0065in., the outer intermediate layer is 0.0005 in., and the outer layer is0.0038 in. thick.

FIG. 2 shows the 0.5 liter multi-layer beverage bottle 40 made from thepreform of FIG. 1. The preform body-forming portion 36 has been expandedto form a transparent biaxially-oriented container body 41. The upperthread finish 34 has not been expanded, but is of sufficient thicknessor material construction to provide the required strength. The bottlehas an open top end 42 and receives a screw-on cap (not shown).

The expanded container body 41 includes an upper conical shouldersection 43 which generally increases in diameter from below the neckfinish flange 35. Below shoulder portion 43 is an indented annular rib44 and then a dome portion 45 which joins at its lower edge to acylindrical panel section 46. The panel section 46 preferably has beenstretched at an average planar stretch ratio of 9 to 12; the virgin PETlayers have an average strain-induced crystallinity of 24 to 32%, andmore preferably of 26 to 30%. The champagne-type base 47 has a standingring 48 which surrounds a central push-up dome 49.

FIG. 3 shows a cross-section of the container panel wall 46, includinginner layer 55 of virgin PET, core layer 56 of recycled PET, outer layer57 of virgin PET, and inner and outer intermediate layers 58, 59 of theoxygen-scavenging polymer. In this embodiment, the relative percent bytotal weight of the various layers in the panel section are about 25%for inner layer 55, about 41% for core layer 56, about 28% for outerlayer 57, and the intermediate scavenger layers 58 and 59 together areabout 5.6 weight percent. The container overall contains 7.5 weightpercent of the scavenger. Depending on the application, there may be asubstantially uniform thickness of the scavenger layer throughout thecontainer, or alternatively a relatively greater amount of scavenger inthe panel (thinnest wall portion) over that in the much thicker neckportion and/or base regions, where the greater thickness PET layersprovide sufficient passive barrier protection. Preferably, the scavengerlayer is of substantially uniform thickness in the panel.

This container provides a shelf-life for beer of no greater than 50parts-per-billion (ppb) of oxygen over 112 days (16 weeks), as describedin the following examples.

EXAMPLES

The following examples describe various methods of preparing an enhancedoxygen-scavenging polymer. The scavenging polymer is then used to make anumber of the three-material five-layer (3M/5 L), 500 ml beer bottlespreviously described and shown in FIGS. 1-4. These bottles are testedaccording to an Orbisphere test method (described below) for determiningthe scavenging performance of the container. The results are illustratedin FIG. 5, which show the enhanced oxygen-scavenging performance of acontainer made with the solid-stated polymer of the present invention,compared to prior art monolayer, multi-layer PET/MXD-6, multi-layerPET/EVOH, and glass containers.

Example 1

In this example, an aromatic polyamide oxygen-scavenger (EMS 5227) issolid-stated, combined (tumbled) with a metal compound, and then used toform separate layers of a multi-layer beer container.

40 lbs of EMS 5227 polymer pellets with an IV (in m-cresol solvent) of1.55 is placed in a 1-cubic foot agitated and jacketed vacuum chamber(VB-001 Double Plentary Mixer, Ross, Hauppauge, N.Y.; a 10-cubic footchamber is also available). EMS 5227 is a polymer produced by EMS(located in Domat/EMS, Switzerland) by condensing meta-xylene-diaminewith adipic acid and 11 molar percent isophthalic acid. The amorphous5227 pellets are first dried and crystallized under agitation at 250° F.(120° C.) at 10 torr for 6 hours. By first crystallizing the polymer,the melting temperature is increased to allow an increase in thesubsequent solid-stating temperature. The T_(g) of the polymer is 85° C.In accordance with the solid-stating method to enhance the scavenging,the temperature is then turned up to 350° F. (177° C.) and the pressuremaintained at 10 torr for an additional 42 hours. At the end of thesolid-stating time the temperature of the transfer fluid heater isreduced to sub-ambient (below 25° C.). The polymer is cooled for 1 hourprior to removal. The polymer is transferred to 2-25 lb metal cans withtight sealing lids.

The polymer from one can is tumbled with 2500 ppm ground cobaltneodecanoate pastilles (The Shepherd Chemical Co. No. 03676400) for 4hours. The resulting mixture is used to make two intermediate layers ofthe preforms, which are then reheat stretch blow molded into bottles, asdescribed above with respect to FIGS. 1-4.

75 of the bottles are selected at random, filled with deoxygenated waterand then capped (Alcoa aluminum cap) for Orbisphere testing. Immediatelyafter filling, the samples have about 100 ppb oxygen content. Two tofive days later they are down below 50 ppb. Two to three weeks afterfilling, they are below 20 ppb and remain there for a long period oftime, much longer than 16 weeks (112 days)—see FIG. 5.

Measurements of Oxygen-Scavenging Rate

The Orbisphere test components are available from Orbisphere, Geneva,Switzerland.

The following is a summary of the test procedure.

1. An 80-gallon stainless steel pressure tank is filled with tap water.It is then sparged with nitrogen at a high rate, around 40 liters perminute, for 1 hour. This takes the concentration of oxygen down from8000 ppb to under 100 ppb. After sparging, the tank is held at 22 psi ofnitrogen.

2. Each of 75 500 ml beer bottles is loaded onto an Orbisphere bench topbottle filler and is sparged with nitrogen at a rate of 20 liters perminute for a period of 30 seconds to remove oxygen from the bottle. Eachbottle is filled with the de-oxygenated water from the tank. The bottleis then removed from the filler and set on the bench. There is about a15 cc headspace created by the displacement of the fill tube of thefiller device.

3. A 28 mm Alcoa aluminum cap with a PET-compatible (EVA) liner isscrewed onto the top of the bottle. The cap is backed off slightly whilethe bottle is squeezed by hand until the gas in the headspace of thebottle is squeezed out. Once the gaseous headspace has all been removed,the cap is again tightly twisted by hand onto the thread finish of thebottle.

4. After all 75 bottles have been filled, 5 are taken by random andplaced in the Orbisphere model 29972 sample device connected to anOrbisphere model 3600 analyzer. The bottle cap is punctured, a tube isdropped to the bottom of the bottle, the bottle headspace is pressurizedwith 20 psi nitrogen, and the liquid is forced out of the bottle andthrough the Orbisphere analyzer sensor at a rate of 0.13 liters perminute. When 30-50% of the liquid has been removed from the bottle, themeasurement is stable and the displayed number is recorded. The resultsof 5 bottles are averaged to support a trend analysis. Note there is afixed headspace of 3% in these bottles; the headspace reappears over 34days after filling as the nitrogen (from sparging the tank water),leaves the water in the bottle and enters the headspace.

5. bottles are tested according to the following approximate schedule: 1day, 3 days, 7 days, 11 days, 2 weeks, 4 weeks, 6 weeks, 8 weeks, 12weeks, 16 weeks, 20 weeks, 24 weeks, 28 weeks, 32 weeks. Data isrecorded and graphed for trend analysis to determine suitability for abeer package.

The Orbisphere results are shown in FIG. 5, which is a graph of theamount of oxygen in the liquid exiting the container, in parts perbillion (ppb), versus the time, in weeks. As indicated, the bottles havebeen filled with deoxygenated water and are held in an environment at72° F. (22° C.) and 50% relative humidity.

A desired specification for beer is represented by the dashed line inFIG. 5—i.e., the Orbisphere results described above where the 600 ppb isthe O₂ content of the water. Thus, the desired specification is for theoxygen content in the water to remain below 600 ppb. This defines the O₂shelf life for the container. It means that the oxygen present duringfilling, and that which permeates through the sidewall and/or leaks inthrough the cap and enters the liquid, must remain below 600 ppb duringthe entire 112 day period.

The oxygen performance of various prior art containers are alsoillustrated in FIG. 5. All of the containers used an Alcoa aluminum cap(nonreactive, threaded, with a PET compatible liner). A first prior artcontainer A is a monolayer PET control container made from a singlelayer of virgin bottle-grade PET, having a thickness of 15 mils (0.015in.), a diameter of 2.6 in., and a height of 4.75 in.; the estimatedsurface area of the container is about 60 in. squared. As shown in FIG.5, the monolayer container exceeds the 600 ppb specification at about 1¼week.

A second prior art container B is a two-material, five-layer (2M/5 L)container made from virgin PET as the inner, outer and core layers, andMXD-6 nylon (which has not been solid-stated) as the inner and outerintermediate layers. The MXD-6 comprises three (3) weight percent of thecontainer. This container has the same thickness and dimensions as thecontrol container. This container fails (exceeds) the specification atabout 4 weeks.

A third container C is a two-material, five-layer (2M/5 L) containermade from virgin PET (inner, outer and core layers) and EVOH (inner andouter intermediate layers). The EVOH comprises three (3) weight percentof the container. This container falls outside the specification atabout 11 weeks.

A fourth container D is a glass container. This container stays withinthe specification for 24 weeks. There is oxygen leakage around the capinto the container, producing a gain in oxygen content over time.

The container E of the present invention (7½% by weight solid-statedMXD-6 of the total container weight), has a reduction in oxygen contentover time and a much lower level of oxygen concentration than the glasscontainer. The oxygen concentration stays substantially below 20 ppb formost (all but the first week) of the 24 weeks. This is well beyond the16-week requirement. During the first week the O₂ present during fillingis being scavenged at an enhanced rate as illustrated in FIG. 7(discussed below).

The box in the upper right corner of the graph of FIG. 5 shows athree-week trend analysis, comparing the prior art containers with thecontainer of the present invention. Listed in the box are values foroxygen gain per day in ppb of O₂. As shown, the container of thisinvention has a negative gain of −3.4 ppb/day (trend in 3 weeks). Thesecond best container is the glass container, having a +2.1 ppb gain perday. The other container values are +6, 18 and 43 ppb/day. Thus, thereis a significant improvement even in the first three weeks of the test.

FIG. 6 is an exploded view comparing the scavenging performance over thefirst 40 days. Again, the monolayer PET container A′ exceeds the 600 ppbbetween 10-15 days. Two containers E′-1 and E′-2 of this invention startat about 50-100 ppb and rapidly drop below 20 ppb in about 5-7 days.Note that FIGS. 5-6 show the Orbisphere test results, which measures theO₂ content of the fluid. In use, a typical aseptically-filled beerbottle may have an initial total package O₂ content of 200 ppb (includesO₂ in beer and headspace), which would drop to 34 ppb (total package) in5-7 days due to the scavenging effect of the package. The initial 200ppb total package O₂ content seen by the brewer is close to the 100 ppbliquid O₂ content (Orbisphere) value (where the liquid has an O₂ contentof 100 ppb, the total package O₂ content (including liquid andheadspace) would be 170 ppb).

FIG. 6 also shows the scavenging performance (over the first 35 days) ofa multi-layer PET/MXD-6 container B′ without solid-stating (close to 600ppb at ˜35 days), and a multi-layer PET/MXD-6 container F′ where theMXD-6 has been solid-stated but no metal is used (exceeds 600 ppb at ˜30days).

FIG. 7 also illustrates the enhanced scavenging rate of the polymer ofthis invention. Here a sample container (from Example 3—containingsolid-stated MXD-6, tumbled, 7½ weight percent) was filled withoxygenated (normal tap water) having a dissolved O₂ content of about9000 ppb. The scavenging polymer reduced the O₂ content to below 6500ppb in 24 days, at a rate of 175 ppb/day. This is an extremely high rateof scavenging. Additional tests were run to determine the effect of thesolid-stating process. They are described below and illustrated in FIGS.8-15.

IR Spectroscopy

FIGS. 8A-8B show the results of infrared (IR) spectroscopy conducted onan MXD-6 sample without solid-stating (8A) and after solid-stating for60 hours (8B). The ordinate is % transmittance, and the abscissa iswavenumbers (cm⁻¹). There is substantially no difference (between 8A and8B) and thus the solid-stating appears to have no effect on the polymerstructure.

NMR

FIGS. 9A-9B show the results of nuclear magnetic resonance (NMR) on anMXD-6 sample without solid-stating (9A) and after solid-stating for 48hours (9B). Again, there is substantially no difference and thus thesolid-stating apparently has had no effect on the chemical structure.The NMR test was performed on samples after each 4-hour interval (over atotal 60-hour solid-stating process) and substantially no difference wasnoted between any sample during the entire time.

Molecular Weight

The following discussion of molecular weight determination is taken fromthe published literature of LARK Enterprises, Inc., 12 WellingtonStreet, Webster, Mass. 01570.

The physical characteristics of polymers are determined by theirchemistry and the size of the molecules. The chemistry affectscharacteristics such as solubility and adsorption of various metals,chemical and thermal resistance to degradation, conductivity, andadhesion. The size of the polymer molecules correlate to its rheology,or flow properties under stress conditions.

There are a number of statistical averages used by polymer scientists todescribe the properties of polymers. The ones presented here arecorrelated to certain physical properties. Brittleness and ease of flowincrease with decreasing Mn (number average molecular weight). Thetensile strength and hardness increase with increasing Mw (weightaverage molecular weight). Flex life and stiffness increase withincreasing Mz (Z average molecular weight). These averages can beobtained from a variety of separate testing procedures. End grouptitration, freezing point depression, boiling point elevation, osmoticpressure, or fractional vapor pressure change could be used to determinethe Mn. Light scattering or viscosity could be used to determine the Mw.Ultracentrifugation can be used to determine Mz. There are othermolecular weight averages used such as Mv (usually nearly equal to Mw)and ratios of averages, however, the three averages that are the mostprevalent are Mn, Mw and Mz. The ratio of Mw/Mn is known as thedispersity of the polymer and is an estimate of the breath of themolecular weight distribution. Samples with a dispersity of close to oneare considered to be nearly homogeneous. Anionically polymerized styrenewith dispersities of 1.01 to 1.07 are generally used to calibrate GPCinstruments. It should be noted that the dispersity of a polymergenerally reflects its mode of synthesis and can varywidely—dispersities greater than 20 are not uncommon.

The technique of GPC (Gel Permeation Chromatography) or SEC (SizeExclusion Chromatography), two names that can be used interchangeably,has the advantage of being able to determine multiple parameters fromone analysis. The method is applicable to all polymers that are soluble.The method of analysis uses about ten milligrams of sample (or less)dissolved in four milliliters of solvent. The dissolved polymers arepumped under high pressure (and in some cases high temperature to keepthe polymer in solution) through a series of tubes packed with gel ofvarying pore size. In contrast to a mechanical sieve, the sieving actionoccurs with the larger molecules not fitting in the pores and elutingfirst while the smaller molecules elute last. The actual comparisons ofsamples and standards are made based on the size of the molecules insolution. Other than for the most exacting work the hydrodynamic radiuscomparisons are used directly or with minimal corrections. The time orX-axis can be calibrated logarithmically according to the size of themolecule in solution. The largest molecules are seen on the left of thechromatogram and the smallest at the right. This comparative nature ofGPC requires the routine calibration of the instrument with well-definedstandards. A curve is fit to the experimental standards and themolecular weight averages of interest are then calculated.Mn=n ₁ *M ₁ /Σn _(i) +n ₂ *M ₂ /Σn _(i) +n ₃ *M ₃ /Σn _(i)+ . . .Mw=n ₁ *M ₁ *M ₁ /Σn _(i) *M _(i) +n ₂ *M ₂ *M ₂ /Σn _(i) *M _(i) +n ₃*M ₃ *M ₃ /Σn _(i) *M _(i)+ . . .Mz=n ₁ *M ₁ *M ₁ *M ₁ /Σn _(i) *M _(i) *M _(i) +n ₂ *M ₂ *M ₂ *M ₂ /Σn_(i) *M _(i) *M _(i) +n ₃ *M ₃ *M ₃ *M ₃ /Σn _(i) *M _(i) *M _(i)++ . .. .Disp.=Mw/Mn

n₁=number of molecules with molecular weight M₁

M₁=molecular weight of an individual molecule

n_(i)=total number of molecules in the sample

In addition to the averages obtained from the same sample, GPC has theadvantage of giving a graphical representation of the mass as a functionof molecular weight. The chromatogram that results is a good tool toquickly see trends in data that would not be immediately obvious.

FIG. 10 shows a GPC curve (chromatogram) for an MXD-6 sample which hasnot been solid stated.

FIGS. 11-13 and Table 1 below show the results of a GPC for asolid-stated MXD-6 sample taken at 4-hour intervals during a total60-hour solid-stating process according to the following parameters:

TABLE 1 Mn Mw Mz Mp Disp. 1-0  21902 48232 66320 51361 2.20 1-4  2189548605 66864 51361 2.22 1-8  22511 50102 68921 52546 2.23 1-12 * * * * *1-16 23117 51953 71243 55677 2.25 1-20 23113 52343 71566 57311 2.26 1-2423028 52709 72271 57311 2.29 1-28 22824 52713 72355 58028 2.31 1-3223256 53905 74660 58998 2.32 1-36 23642 54369 74559 60367 2.30 1-4024296 53865 74239 58893 2.22 1-44 24895 55457 76255 61642 2.23 1-4823882 54212 74923 59253 2.27 1-52 24449 56596 78701 63455 2.31 1-5625088 56379 78076 63200 2.25 1-60 23620 55542 76921 62553 2.35 * Sampleerror

FIGS. 11-13 show the rise in Mn, Mw and Mz respectively over time duringsolid-stating. The rise in Mn establishes that the lower molecularweight (shorter) chains are increasing in length. The rise in Mz, at agreater rate than Mn, establishes that the higher molecular weight(longer) chains are also increasing in length (and at a greater rate).There is also a rise in Mw. Thus, the molecular weight of the MXD-6 isincreasing during solid-stating in this embodiment.

The last column of Table 1 (above) is the polydispersity number, whichreflects the distribution of molecular weight (as opposed to anaverage). This value is obtained by dividing Mw by Mn. To those skilledin the art it is apparent that there is no significant change in thisratio over the solid-stating time. It was also determined that there wasno significant change in the cyclic oligomer component of the MXD-6polymer.

FIG. 14 and Table 2 below show the change in intrinsic viscosity (IV)for an MXD-6 sample A, taken at 4-hour intervals over the solid-statingtime:

TABLE 2 Time (hours) A 0 1.1418 4 1.1463 8 1.1564 12 1.1822 16 1.2010 201.1939 24 1.2023 28 1.2085 32 1.2152 36 1.2315 40 1.2447 44 1.2473 481.2588 52 1.2621 56 1.2737 60 1.2772

FIG. 14 shows the results of IV as a function of solid-stating time fora sample of MXD-6 6007 which has been solid-stated at 10 torr vacuum and350° F. (177° C.) for a time from 0 to 60 hours. The IV increased at arate of 0.0023 dl/g per hour. The sample taken at 48 hours of processingtime, combined with cobalt, has the superior scavenging rate illustratedin FIGS. 5-7.

Example 2

The second can of polymer from Example 1 is extrusion compounded withthe metal compound. The polymer pellets are compounded with 2500 ppmcobalt neodecanoate pastilles. (The Shepherd Chemical Co., Cincinnati,Ohio, cat. no. 03676400), stranded, chilled under water and then choppedinto pellets. This material is then placed back in the 1-cubic footreactor and processed at 250° F. (120° C.) and 10 torr vacuum withagitation for 12-16 hours. This step is required to dry and crystallizethe material to enhance the injection molding process. Wet amorphousmaterial will not form proper layers and will nucleate the adjacentlayers of PET to form haze (nontransparent). This material is thenprocessed into preforms and bottles the same as in Example 1. Filledbottles were tested on the Orbisphere and exhibited substantially thesame oxygen performance as Example 1.

Example 3

In this example, MXD-6 6007 (Mitsubishi Chemicals, Japan) is substitutedfor the EMS 5227 in Example 1. Since the MXD-6 6007 is crystalline asreceived, the initial lower temperature drying process was notnecessary. The polymer was processed at 350° F. (177° C.) and 10 torrfor the entire 48 hours. All 55 lbs (the standard weight of a bag ofMXD-6) was loaded into the reactor. The resulting solid-stated polymerfilled both of the 25 lb cans (with about ½ of a 5-quart can left over).One can (25 lbs) of this material was then tumbled with 2500 ppm ofground cobalt neodecanoate pastilles (The Shepherd Chemical Co. No.03676400) and then processed into preforms and bottles as described inExample 1. Filled bottles were tested on the Orbisphere and exhibitedsubstantially the same oxygen performance as Examples 1 and 2.

Example 4

This is the same as Example 3 except the second can of solid-statedMXD-6 from Example 3 was extrusion compounded as in the process ofExample 2. Bottles tested by the Orbisphere method exhibited the sameexcellent performance as Examples 1-3.

Example 5

In this example, meta(m)-xylenediamine (MXDA), isophthalic acid andadipic acid are copolymerized in solution, with water catalyzing thepolymerization reaction, and cobalt neodecanoate is combined therewithas the metal. Sodium hypophosphite is added later in the reaction toincrease the molecular weight (see WO92/02584 to Eastman Chemical). Theresulting copolymer (with dispersed cobalt) has an IV of about 0.88(60/40 phenol/1,1,2,3-tetrachloro-ethane solvent); it is then granulatedand solid-stated as 350° F. (177° C.) for 48 hours to raise themolecular weight (IV=0.99).

More specifically, 656 g of MXDA (CAS no. 1477-55-0), 113.6 g ofisophthalic acid (CAS no. 121-91-5), 604 g adipic acid (CAS no.124-04-9), 3 grams cobalt neodecanoate (CAS no. 27253-31-2), and 1000 gof water are mixed in a 4-liter glass 2-neck 2-piece reaction vessel.The reaction chamber is placed in a mantle and the mantle temperature israised to 400° F. (205° C.) with paddle agitation at 50 RPM (revolutionsper minute) under an 8.5 psi (0.586 bars) nitrogen blanket. A smallstream of the nitrogen is split off of the top to remove water and anyvolatile byproducts. After one hour the mantle temperature is raised to500° F. (260° C.). After 2½ hours the temperature is raised to 575° F.(300° C.). After 30 minutes the pressure is dropped to 6 psi (0.414bars). After 30 minutes the pressure is dropped to 4 psi (0.276 bars).After 30 minutes the pressure is dropped to 1 psi (0.0689 bars) and 6grams of sodium hypophosphite powder (CAS no. 123333-67-5), is dissolvedin 20 cc (cubic centimeters) of water and then injected into thereaction. The reaction is continued until the torque on the agitatorreaches 500 in-oz (36,000 cm/g) at 50 RPM. Then the heat is removed andthe agitation is shut off. The sample is allowed to cool to roomtemperature under 6 psi (0.414 bars) of nitrogen.

The polymer has an IV of about 0.80 dl/g (60/40phenol/1,1,2,3-tetrachloro-ethane solvent). The IV is increased bysolid-stating as described below.

The polymer is cut off of the paddle with a band saw and is thengranulated to a medium texture with a high level of fines using a modelGran 220 bench grinder (Dynisco/Kayeness, of Morgantown, Pa.) with a 10nun screen. The granulated polymer is then spread in a Pyrex oven panand solid-stated in a vacuum oven at 350° F. (177° C.) at 1 torrpressure for 48 hours.

The IV of the solid-stated polymer is about 1.2, and has a melt index inthe range of 15-35 grams per 10 minutes in the 50-100 ppm moisture range(ASTM #D1238-89 with a 2.16 kg total weight and a 0.0825 inch (2.0955mm) diameter orifice at 275° C.).

The solid-stated scavenging polymer is then fed into a sequentialmulti-layer injection molding apparatus to produce 3M/5 L performs (asper FIGS. 1-4) having inner and outer layers of virgin PET (Shell 8006,0.81 IV nominal, 2 molar percentage isophthalic acid copolymer,available from Shell Oil Co., Houston, Tex., USA), a core layer ofpost-consumer PET (IV=0.74 dl/g), and inner and outer intermediatelayers of the scavenging polymer.

The preforms are blown into 500 ml bottles and subjected to theOrbisphere test (same as Example 1). The results show an initial oxygenconcentration in the fluid after 24 hours of around 100 ppb, dropping tounder 40 ppb within 4 days, down under 20 ppb within 1 week andremaining under 20 ppb, for a period of six months (26 weeks).

Example 6

In this example, an aromatic ester alpha-hydrogen carbonyl is thescavenging polymer. The aromatic ester polymer is prepared frombisphenol A diacetate and suberic acid in accordance with the processdescribed below and illustrated in FIG. 16.

FIG. 16 shows the condensation of bisphenol-A diacetate and adipic acidto make a polymer having two alpha-hydrogen carbonyl groups, two esters,one aromatic backbone structure (with two rings), and a 4-carbon chainaliphatic group. This polymer has relatively high T_(g) of 91° C. Amodified polymer made with suberic acid (as opposed to adipic acid) hasa lower T_(g) of 79° C., which is in the preferred range for use withPET orientation temperatures.

The following process may be used to prepare a polymer from bisphenol Adiacetate and suberic acid (see for example Preparative Methods OfPolymer Chemistry, 2nd Edition, Sorensen, Campbell, page 149):

In a first step, diacetate of bisphenol A is prepared by dissolving 11 g(grams) of bisphenol A in a solution of 9 g (0.22 mole) sodium hydroxidein 45 ml water in a 250 ml Erlenmeyer flask. The mixture is cooled in anice bath and a small quantity of ice is added to the flask. Then, 22.4 g(0.22 mole) acetic anhydride is added and the flask is shaken vigorouslyin an ice bath for 10 minutes. The white solid is filtered, washed withwater, and recrystallized from ethanol.

A mixture of bisphenol A diacetate 312 g (1 mole), suberic acid 174 g (1mole), 0.60 g toluenenesulfonic acid (monohydrate) is placed in a2-liter, 2-neck flask with agitator. The flask is purged with nitrogenwhile agitating for 20 minutes. The temperature is then raised to 180°C. while agitating and purging with nitrogen at ambient pressure. Aceticacid distills as the temperature is slowly raised from 180° C. to 250°C. while the pressure is slowly reduced to about 1 torr. The melt ismaintained at 250° C. and 1 torr for 1 hour.

When using an aliphatic acid, it may be advantageous that pyridine besubstituted for sodium hydroxide and water in the above reaction.

The polymer may be extrusion compounded with cobalt neodecanoate andsolid-stated, as follows. Thirty pounds of the aromatic esteralpha-hydrogen carbonyl polymer is compounded on an extruder with 2500ppm cobalt neodecanoate, stranded and cut into pellets. The extruder hasa 1½ in. diameter and a 36:1 L/D ratio and a compression ratio of 3:1.The entire transition zone is of a barrier design with a 0.010 in.clearance between the screw and barrel. The output of the extruder isdirected into a stranding dye; molten strands are then pulled through awater bath for cooling, and are finally chopped into ¼ in. long by ⅛ in.diameter pellets. The pellets are then placed in a 1-cubic footjacketed, agitated, vacuum reactor (VB-001 Double Plentary Mixer, Ross,Hauppauge, N.Y.) and heated to 250° F. (120° C.) for 3 hours under 10torr vacuum with agitation to dry and crystallize the pellets. Thetemperature is then raised to 470° F. (240° C.) at a pressure of 10torr, solid-stating the pellets for an additional 36 hours. The pelletsare then cooled and loaded into a sequential multi-layer injectionmolding apparatus for making 3M/5 L performs (same as Example 1), andblown into bottles (same as Example 1). The bottles are expected to havean oxygen performance similar to Example 1.

Example 7

In this example, the cobalt is added to MXD-6 6007 in the solid-statingreactor (after the MXD-6 has been solid-stated). This method has severalbenefits over that described in Example 1.

55 lbs of MXD-6 is solid stated as described in Example 3, except thetemperature is 205° C. and the pressure is 0.1 torr. Table 3 shows theintrinsic viscosity as a function of solid-stating time, where theintrinsic viscosity has been determined with each of 60/40phenol/1,1,2,3-tetrachloroethane as the solvent and m-cresol as thesolvent.

TABLE 3 IV (60/40 phenol/1,1,2,3- Time (hours) tetrachloroethanesolvent) IV (m-cresol solvent)  0 h 1.154 1.689  8 h 1.184 1.725 24 h1.245 1.776 48 h 1.268 1.800 54 h 1.347 1.867

Cobalt neodecanoate pastilles (not ground) are added at 2500 ppm to thesolid-stated MXD-6 in the solid-stating reactor and the material isagitated under vacuum at 300° F. (150° C.) for 30 minutes. The materialis cooled in the reactor for 1 hour and stored in a covered can sealedunder ambient atmosphere.

This process can provide a more uniform cobalt coating on the surface ofthe MXD-6 pellets, resulting in better scavenging performance. There isno need to grind the cobalt neodecanoate pastilles. Also, because theprior method involved transferring the MXD-6 from the solid-statingreactor to a tumbling vessel for addition of cobalt, excess moisturecould be extracted from the atmosphere by the polymer during suchtransfer; it would thus be beneficial to dry such mixture prior toinjection molding. In contrast, by adding the cobalt directly to theMXD-6 in the solid-stating reactor, there is less need for a subsequentdrying procedure.

Example 8

In this example, the oxygen-scavenging performance is compared forplaques made from either solid-stated, or non-solid-stated, polyamidehaving a cobalt neodecanoate concentration of 2500 ppm (500 ppm cobalt).

The solid stating is carried out as described in Example 1, for 48hours. The plaques are tested according to the wet plaque testpreviously described under “Performance Tests”.

FIGS. 15A-15D illustrate the oxygen-scavenging performance (% oxygencontent in the jar) for plaques of solid-stated and non-solid-statedpolymers as a function of time in days. In FIG. 15A, the data for thenon-solid-stated MXD-6 6007 is shown as line 100; the solid-statedplaque data is shown as line 101. In FIG. 15B, the data for thenon-solid-stated MXD-6 6001 is shown as line 102; the solid-statedplaque data is shown as line 103. In FIG. 15C, the data for EMSnon-solid-stated is shown as line 104; the solid-stated plaque data isshown as line 105. In FIG. 15D, the data for nylon 6 non-solid-stated isshown as line 106; the solid-stated plaque data is shown as line 107.

From FIGS. 15A-D it is seen that the solid-stated oxygen-scavengingpolymers exhibit enhanced performance compared to the non-solid-statedscavenger. This enhanced performance is evidenced by the greater (morenegative) slopes of the respective lower lines and the resulting lowerlevels of measured percent oxygen content over time.

Example 9 Material Distribution in Bottle

Table 4 below shows the effect of solid-stating time (8, 20 and 36hours) on the distribution of scavenger material in the neck finish(flange 35 and above in FIG. 2), body (the cylindrical sidewall 46), andthe neck (the shoulder portion 43 between the finish and body) in the5-layer bottle embodiment. The third example in Table 4, solid statingfor 36 hours, resulted in the greatest percentage of scavenger in thebody (the thinnest wall portion of the container), providing the bestscavenging performance.

TABLE 4 Barrier Distribution in Finish, Neck, and Body of Bottle example1 2 3 hours of solid-stating 177° C., 3 torr 8 20 36 barrier layer % inbody 3.63 5.07 5.83 IV 0.971 1.16 1.25 finish weight complete (g) 6.7256.725 6.725 neck weight complete (g) 4.755 4.755 4.755 body weightcomplete (g) 18.99 18.99 18.99 end cap not used (g) 2.96 2.96 2.96 gramsof barrier in finish 0.934 0.722 0.716 grams of barrier in neck 0.4830.388 0.382 grams of barrier in body 0.689 0.963 1.107 total grams inneck + body 1.172 1.351 1.49 total grams in bottle 2.106 2.073 2.206 %of barrier in finish 13.88 10.73 10.65 % of barrier in neck 10.15 8.1528.04 % of barrier in body 3.63 5.07 5.83 % of barrier in neck + body4.936 5.687 6.272 % of barrier in bottle 6.30 6.20 6.60

Example 10

In this example, samples of the 5-layer bottle previously described werefilled with tank water (100 ppb oxygen). The scavenger in the bottleswas solid-stated at 350° F. (177° C.) for a period of time ranging from0 h to 60 h. FIG. 17 illustrates the oxygen concentration of the watercontained in each bottle. It can be seen that within the first 8 hours,there was a very sharp reduction in oxygen content. Thus, even withoutan extended solid-stating time, and before a substantial increase in IVhas occurred, there is a remarkable increase in scavenging performanceobtained by the solid-stating process of this invention.

Example 11

In this example, the effects on oxygen-scavenging performance areillustrated where the scavenging polymer, MXD-6 6007, is prepared bydifferent methods and incorporated as two layers in the 5-layer bottlepreviously described. The results for both tap water and tank water aredisplayed in Tables 5A and 5B, after 3 weeks and 9 weeks, respectively.

The different methods are designated by column headings A-D as follows:“A” indicates that the scavenger comprises only MXD-6 6007 without anycobalt; “B” indicates that 2500 ppm cobalt neodeconoate as a powder (500ppm cobalt) has been tumbled into the MXD-6 6007 at 150° C. for 30minutes; “C” indicates that the same amount of cobalt has been added tothe MXD-6 6007 but in the solid-stating vessel and tumbled; “D”indicates that the cobalt has been added as in “C” followed by anadditional step of subjecting the polymer to a vacuum of 0.1 torr at 63°C.

The headings for each row are: “Air Dry,” indicates that the polymer hasbeen subjected to air-drying 130° C.; “Vac Dry” indicates that thepolymer has been subjected to a vacuum of 2.1 torr at a temperature of150° C.; and “SS” indicates that the polymer has been solid-stated at205° C. for 48 h at 0.1 torr.

The bottles are filled with either tap water (O₂ concentration ˜8600ppb) or tank water (O₂ concentration ˜100 ppb). By three weeks, theoxygen concentration of the water is measured by the Orbisphere methodand these results are tabulated in Table 5A; similarly the 9-weekresults are tabulated in Table 5B.

The data of Tables 5A-5B shows the advantageous effects of solid-statingin combination with the addition of cobalt to the polymer (row SS,column D). The improved oxygen-scavenging performance is especiallynoted for the tank water results where the dissolved oxygen contentsteadily decreases in each of “B” to “C” and “D” (row SS).

TABLE 5A OXYGEN CONCENTRATION AFTER 3 WEEKS (ppb) TapWater - 8600 ppbTankWater - 100 ppb A B C D A B C D Air Dry 7100 7100 7100 7100 780 700450 450 Vac Dry 6900 7000 7200 6600 560 450 380 240 SS 7000 4400 49004200 540 35 15 4

TABLE 5B OXYGEN CONCENTRATION AFTER 9 WEEKS (ppb) TapWater -8600 ppbTankWater - 100 ppb A B C D A B C D Air Dry 6483 5677 5108 4705 17921457 840 980 Vac Dry 6498 5254 5418 4076 1162 867 686 550 SS 5985 9731377 870 1222 21 19 1

Example 12

The following example illustrates a selection technique for the amountof metal in the enhanced oxygen scavenger.

The oxygen-scavenging performance of EMS FE5270 nylon (MXD-6 6007 solidstated at 193° C. for 16 hours under nitrogen) was studied at varyingconcentrations (0, 50, 100, 200, 300, 400, 500, 600, 700, 800, 900,1000, 1500, and 2000 ppm) of cobalt (cobalt neodecanoate (CoNeo)concentration=cobalt concentration*5). Plaque samples (as previouslydescribed in the wet plaque test) for each concentration were preparedby heat-treating the resins in a 10 cubic foot vertical blender (ROSSV-10 Vertical blender) at 150° C. for 12 hours. Once the samples werecooled to room temperature, the appropriate amount of cobaltneodecanoate was added. Each sample was then tumbled in a metal paintcan for about 30 minutes. To drive out any remaining moisture in thematerial, each sample was then redried in a vacuum drier at 62° C. forabout 24 hours.

To compare wet and dry conditions, half of the plaque samples for eachconcentration were placed in jars according to the wet plaque testpreviously described, and the other half were placed in jars accordingto a “dry plaque test” (same as wet plaque test but no water in thejars). Oxygen testing was done approximately twice per week for 54 days;the dry and wet results are listed in Tables 6A-6B respectively andillustrated in the bar graphs of FIGS. 18-19 respectively.

As shown in FIGS. 18-19, the wet plaque test samples displayed a higheroxygen-scavenging performance than the dry plaque test samples. After 54days, none of the dry samples displayed greater than a 1.6% oxygenreduction, whereas the oxygen content in some of the wet samples wasreduced by amounts greater than 5%. For the wet samples, optimumperformance occurred with a cobalt concentration of 500 ppm with a 5.57%total oxygen reduction. Each of the wet samples from 300 to 1000 ppm hadclose to or greater than 5% reduction.

FIGS. 21-22 are bar graphs of percent oxygen reduction vs. sampleconcentration for dry and wet samples respectively, illustrating theeffect of cobalt concentration (from 0 to 850 ppm cobalt based on thenylon) for three different processing techniques: solid-stated (darkshaded bars); vacuum dried (light shaded); and air dried (white bars).The dry samples (per the dry plaque test) showed similar percent O₂reduction for all three processes, none greater than 0.60. In contrast,the wet samples (per the wet plaque test) from the solid-stated processshowed a clearly superior result, both compared to the dry samples andcompared to the other two processes. The air dried and vacuum driedsamples were made from MXD-6 6007. The solid-stated samples were madefrom EMS nylon as previously described, except the resin washeat-treated in the blender for 11 hours and re-dried in the vacuumdryer at 62° C. for 4 hours.

TABLE 6A Average Oxygen Content (%) Over 54 Days for Dry Plaque TestSample (PPM) 1 Day 4 Day 9 Day 15 Day 18 Day 22 Day 25 Day 29 Day 32 Day36 Day 38 Day 43 Day 54 Day 0 21.0 21.1 21.0 21.1 21.0 21.2 21.0 21.121.2 21.0 21.1 21.1 21.0 50 21.0 21.1 21.0 21.1 21.0 21.1 21.0 21.0 21.020.8 20.8 20.9 20.9 100 21.0 21.1 21.0 21.0 20.3 21.0 21.0 21.0 21.020.8 20.8 20.9 20.8 200 20.9 20.9 20.7 20.6 20.5 20.5 20.4 20.4 20.320.1 20.1 20.1 20.0 300 20.7 20.9 20.6 20.4 20.6 20.5 20.5 20.5 20.520.4 20.2 20.3 20.2 400 20.8 20.8 20.7 20.4 20.6 20.4 20.5 20.4 20.420.2 20.1 20.2 20.1 500 20.8 20.9 20.6 20.4 20.5 20.2 20.3 20.2 20.120.0 19.8 19.9 19.7 600 20.8 20.8 20.6 20.4 20.4 20.2 20.2 20.1 20.119.9 19.8 19.8 19.7 700 20.8 20.8 20.6 20.5 20.5 20.2 20.4 20.3 20.320.0 19.9 20.1 19.9 800 20.8 20.8 20.6 20.4 20.4 20.2 20.2 20.2 20.119.8 19.8 19.8 19.7 900 20.8 20.8 20.7 20.6 20.6 20.4 20.4 20.4 20.320.1 20.1 20.1 20.0 1000 20.8 20.8 20.6 20.4 20.4 20.2 20.2 20.1 20.119.9 19.8 19.8 19.7 1500 20.8 20.7 20.6 20.4 20.4 20.2 20.1 20.1 20.220.0 19.8 19.9 19.8 2000 20.8 20.9 20.8 20.5 20.6 20.4 20.4 20.3 20.420.1 20.0 20.0 20.0

TABLE 6B Average Oxygen Content (%) Over 54 Days for Wet Plaque TestSample (PPM) 1 Day 4 Day 9 Day 15 Day 18 Day 22 Day 25 Day 29 Day 32 Day36 Day 38 Day 43 Day 54 Day 0 20.8 20.9 20.9 20.8 20.9 20.9 20.7 20.920.9 20.7 20.7 20.7 20.9 50 20.8 20.8 20.8 20.6 20.7 20.6 20.6 20.6 20.620.4 20.3 20.4 20.4 100 20.7 20.6 20.5 20.3 20.2 20.1 20.0 19.9 19.919.5 19.6 19.4 19.3 200 20.4 20.3 19.9 19.7 19.6 19.2 19.0 18.8 18.618.1 18.1 17.9 17.5 300 20.3 20.0 19.6 19.3 19.1 18.6 18.3 18.0 17.717.2 17.2 17.0 16.4 400 20.4 20.0 19.7 19.3 19.1 18.5 18.2 17.8 17.617.0 17.0 16.7 16.1 500 20.5 20.3 20.0 19.5 18.7 18.1 17.9 17.4 17.116.5 16.4 16.1 15.5 600 20.7 20.5 20.3 19.8 19.1 18.4 18.1 17.7 17.416.9 16.6 16.2 15.6 700 20.7 20.5 20.3 20.0 19.3 18.6 18.3 17.8 17.516.8 16.7 16.3 15.7 800 20.7 20.4 20.3 19.8 19.2 18.5 18.2 17.7 17.416.8 16.7 16.4 15.8 900 20.6 20.6 20.6 20.0 20.4 19.8 19.0 18.6 18.117.5 17.3 16.8 16.2 1000 20.6 20.6 20.5 20.2 20.2 19.6 19.3 18.6 18.517.9 17.5 17.1 16.3 1500 20.7 20.6 20.6 20.3 20.4 20.0 19.9 19.6 19.418.8 18.7 18.3 17.4 2000 20.7 20.5 20.6 20.3 20.3 20.2 19.7 19.8 19.719.2 19.0 18.9 18.5

Example 13

The following example further illustrates the effect of increased weightpercentages of the scavenger layers on oxygen-scavenging performance inone embodiment.

MXD-6 was treated as in Example 3; 2500 ppm of cobalt neodecanoate wasadded. The previously described 5-layer bottles were made with varyingweight percentages of the combined two scavenging layers (1%, 2%, 4%,6%, 8%, 10%). Oxygen-scavenging, as measured by the Orbisphere method,was tested for each of tap water (8600 ppb) and tank water (100 ppb).The results are listed in Table 7.

From Table 7, it can be seen that scavenging performance generallydecreases as the amount of the scavenging layer decreases. Optimalamounts of scavenger in this embodiment range from 6% to 10%.

TABLE 7 % Oxygen Content (ppb) Over 91 Days Wt % of 1 wk 2 wk 3 wkoverall MXD-6 slope slope slope slope 1 day 7 days 14 days 21 days 35days 63 days 91 days 10% (tap) 232 51 −33 −56 6575 7881 7463 6320 60624151 2571 10% (tank) −13 −6 −4 0 87 11 9 2 1 34 8 8% (tap) −96 50 31 −307161 6586 7723 7370 6308 5272 4530 8% (tank) −11 −4 −2 0 68 3 1 0 6 4 16% (tap) −141 50 35 −33 7175 6328 7759 7423 6323 5287 4144 6% (tank) −10−3 −2 0 73 13 20 11 3 39 55 4% (tap) −75 64 48 −28 7142 6694 7873 77126785 5722 4658 4% (tank) −3 9 8 4 87 71 190 202 294 420 350 2% (tap) −7174 59 −12 7183 6755 7947 7865 6971 6772 5946 2% (tank) 14 23 22 18 88173 373 500 760 1275 1650 1% (tap) 185 94 47 −25 6900 7826 7782 75046737 5475 5097 1% (tank) 34 29 29 24 195 392 562 763 1147 1801 2278Other Packages (e.g. Juice)

Other applications may allow the use of lesser amounts of the enhancedoxygen-scavenger of this invention and still provide adequateprotection. For example, fruit juice is less oxygen sensitive than beerand thus a lower amount of scavenger may be sufficient. Also, the loweramount may not actually reduce the enclosed oxygen content over time,but simply maintain it at or below some specified upper limit. Thus, theenhanced scavenger is capable of reducing the rate at which the oxygencontent of the container is increased.

In one embodiment, a 5-layer bottle is prepared as previously describedwhere the oxygen-scavenging layer thickness is selected such that theoxygen content of an aqueous liquid is maintained at less than 9,000 ppbfor a designated time period (e.g., 3 months, preferably 6 months), andmore preferably less than 8,000 ppb. The bottle may have an initialoxygen content of 5,000-6,000 ppb, i.e. the oxygen content of thepackage when first sealed.

In one example, a 5-layer bottle for fruit juice may have twointermediate scavenger layers at a total weight percent of 3.5%scavenger in the bottle. During hot filling at 82° C., the headspace isinitially flushed with steam to reduce the initial oxygen content of thebottle.

This bottle can maintain the oxygen content at an acceptable level forat least 3 months. The lower weight percentage of enhanced scavenger isboth cost-effective and provides better delamination resistance and alonger shelf life than prior PET/EVOH bottles.

Other variations of the heat treatment may also produce compositionswith increased scavenging performance but which may only reduce the rateat which the oxygen content in the package is increased, rather thanproviding an actual reduction in oxygen content.

While there have been shown and described several embodiments of thepresent invention, it will be obvious to those skilled in the art thatvarious changes and modifications may be made without departing from thescope of the invention as defined by the appending claims.

1. A method comprising: preparing a composition for use as an oxygenscavenger which comprises a polyamide which has been solid-stated and atransition metal in an amount of at least 200 ppm in the polyamide, themethod comprising the steps of: heat treating the polyamide at atemperature above the glass transition temperature and below the meltingtemperature of the polyamide while under a low oxygen content atmosphereto form a solid-stated polyamide; the polyamide being solid-stated inthe presence of the metal or the metal being added to the polymer afterthe solid-stating step, and wherein the heat treatment increases theoxygen scavenging performance of the composition by a factor of at least1.3 as compared to a composition of the transition metal and the samepolyamide prepared without a solid-stating step.
 2. The method of claim1, wherein the low oxygen content atmosphere has an oxygen content of nogreater than 10%.
 3. The method of claim 2, wherein the low oxygencontent atmosphere comprises an inert gas atmosphere.
 4. The method ofclaim 3, wherein the solid-stating step is carried out at a temperaturefrom 150° C. to 210° C.
 5. The method of claim 2, wherein the atmospherehas a pressure of no greater than 2000 N/m² (15 torr).
 6. The method ofclaim 2, wherein the solid-stating step is carried out for a period ofat least 8 hours at a temperature from 150° C. to 210° C.
 7. The methodof claim 2, wherein the solid-stating step is carried out at atemperature from 150° C. to 210° C.
 8. The method of claim 2, whereinthe solid-stating step is carried out at a pressure of no greater than13.3 N/m² (0.1 torr).
 9. The method of claim 2, wherein thesolid-stating step is carried out at a pressure of no greater than 1333N/m² (10 torr).
 10. The method of claim 1, wherein the amount of thetransition metal is from 200 to 2000 ppm.
 11. The method of claim 1,wherein the amount of the transition metal is from 300 to 1000 ppm. 12.The method of claim 1, further comprising the step, before the solidstating step, of drying the polyamide using at least one of air dryingand vacuum drying, the drying being carried out at a temperature lessthan the glass transition temperature of the polyamide.
 13. The methodof claim 1, wherein the polyamide comprises an aromatic polyamide; analiphatic polyamide; nylon; or an MXD polyamide.
 14. The method of claim1, wherein the heat treatment increases the oxygen scavengingperformance of the composition by a factor of at least 2 as compared toa composition of the transition metal and the same polyamide preparedwithout a solid-stating step.
 15. The method of claim 1, wherein theheat treatment increases the oxygen scavenging performance of thecomposition by a factor of at least 4 as compared to a composition ofthe transition metal and the same polyamide prepared without asolid-stating step.
 16. The method of claim 1, wherein the transitionmetal comprises a compound including the transition metal and a ligand.17. The method of claim 16, wherein the transition metal is a cobaltcompound.
 18. The method of claim 1, wherein, in ambient air, a plaqueformed of the oxygen-scavenging composition has a higher oxygenscavenging rate under wet conditions than under dry conditions.
 19. Themethod of claim 1, wherein the polyamide is a xyliene-substitutedpolyamide; and wherein a ratio of the oxygen-scavenging rate of a plaqueof the oxygen-scavenging composition in an ambient atmosphere containing21% oxygen at 23° C. under wet conditions and under dry conditions isgreater than 2:1.
 20. The method of claim 1, wherein the polyamidecomprises an MXD polyamide and the transition metal comprises cobalt.21. The method of claim 20, wherein the transition metal comprisescobalt carboxylate.
 22. The method of claim 21, wherein the transitionmetal comprises cobalt neodecanoate.
 23. The method of claim 1, whereinthe method includes forming a package having a wall, the wall includingan internal layer comprising the oxygen-scavenging composition, whereinthe package when filled with an aqueous liquid having an oxygenconcentration of 9000 ppb or less and sealed, removes dissolved oxygenfrom the liquid.
 24. The method of claim 23, wherein the package reducesthe dissolved oxygen in the aqueous liquid to an oxygen concentration of200 ppb or less.
 25. The method of claim 24, wherein the packagemaintains the oxygen content of the liquid below 200 ppb for at least 3months.
 26. The method of claim 25, wherein the package comprises aninjection molded multilayer container of a volume no greater than 500ml, and wherein the polyamide comprises an MXD polyamide, the transitionmetal comprises cobalt neodecanoate, and the amount of the cobalt isfrom 200 to 2000 ppm.
 27. The method of claim 26, wherein the containerhas one or more layers comprising polyethylene terephthalate.
 28. Themethod of claim 24, wherein the package maintains the oxygen content ofthe liquid below 100 ppb for at least 3 months.
 29. The method of claim23, wherein the package maintains the oxygen content of the liquid below600 ppb for at least 112 days.
 30. The method of claim 24, wherein thepackage reduces the oxygen content of the liquid at a rate of at least50 ppb/day.
 31. The method of claim 23, wherein the package can bestored unfilled in an ambient atmosphere containing 21% oxygen for atleast 3 months prior to said filling with an aqueous liquid.
 32. Themethod of claim 23, wherein the wall includes at least one layer of theoxygen-scavenging composition and at least one oxygen permeable layer,wherein the oxygen permeable layer is between the oxygen-scavenginglayer and the aqueous liquid.
 33. The method of claim 32, wherein theoxygen permeable layer is also permeable to water.
 34. The method ofclaim 33, wherein water permeates the permeable layer to facilitateoxygen removal by the oxygen-scavenging layer.
 35. The method of claim23, wherein the wall comprises one or more internal layers of theoxygen-scavenging composition between one or more layers of aromaticpolyester polymers.
 36. The method of claim 23, wherein the wallincludes at least one layer of the oxygen-scavenging composition betweenpolyethylene terephthalate layers.
 37. The method of claim 23, whereinthe wall of the package is substantially transparent.
 38. The method ofclaim 23, wherein the package is a substantially transparent multilayerbottle.
 39. The method of claim 38, wherein the bottle includes at leastone internal layer of the oxygen-scavenging composition between layersof aromatic polyester polymers.
 40. The method of claim 23, wherein thepackage is filled with a food or beverage product.
 41. The method ofclaim 23, wherein the package is filled with a tomato-based foodproduct.
 42. The method of claim 23, wherein the package is filled withbeer.
 43. The method of claim 23, wherein the package is filled withjuice.
 44. The method of claim 23, wherein the package comprises aninjection molded container having a multi-layer wall comprising at leasttwo intermediate layers comprising the oxygen-scavenging composition, acore layer between the intermediate layers, and at least two outerlayers having at least one of structural and oxygen barrier properties,where the oxygen-scavenging composition comprises no more than 10% ofthe weight of the package.
 45. The method of claim 44, wherein thepackage is filled with an aqueous liquid having an oxygen concentrationof 200 ppb or less.
 46. The method of claim 44, wherein the two outerlayers comprise polyester.
 47. The method of claim 46, wherein thepolyamide comprises an MXD polyamide and the transition metal comprisesa cobalt compound including a ligand.
 48. The method of claim 47,wherein the outer layers comprise polyethylene terephthalate.
 49. Themethod of claim 48, wherein the package is a substantially transparentmultilayer bottle.
 50. The method of claim 49, wherein the bottle isfilled with beer, juice or a tomato-based food product.
 51. The methodof claim 47, wherein the compound comprises cobalt carboxylate.
 52. Themethod of claim 51, wherein the compound comprises cobalt neodecanoate.53. A method comprising: preparing a composition for use as an oxygenscavenger which comprises a polyamide which has been solid-stated and atransition metal in an amount of at least 200 ppm in the polyamide, themethod comprising the steps of: heat treating the polyamide at atemperature above the glass transition temperature and below the meltingtemperature of the polyamide while under a low oxygen content atmosphereto form a solid-stated polyamide; the polyamide being solid-stated inthe presence of the metal or the metal being added to the polyamideafter the solid-stating step; forming a package having at least oneinternal layer comprising the oxygen-scavenging composition; filling thepackage with an aqueous liquid having an oxygen concentration of 100 ppbor less and sealing the package; reducing and maintaining the oxygenconcentration of the liquid below 100 ppb for 32 weeks; and wherein theheat treatment increases the oxygen scavenging performance of thecomposition by a factor of at least 1.3 as compared to a composition ofthe transition metal and the same polyamide prepared without asolid-stating step.
 54. The method of claim 53, wherein the package isstored unfilled in an ambient atmosphere for at least 3 months prior tosaid filling with the aqueous liquid.
 55. The method of claim 53,wherein the package comprises an injection molded container having atransparent multi-layer wall including the at least one internal layerof the oxygen-scavenging composition and one or more layers ofpolyester.
 56. The method of claim 53, wherein the liquid comprisesbeer, juice or a tomato-based food product.
 57. A method comprising:preparing a composition for use as an oxygen scavenger which comprises apolyamide which has been solid-stated and a transition metal, the methodcomprising the steps of: heat treating the polyamide at a temperatureabove the glass transition temperature and below the melting temperatureof the polyamide while under a low oxygen content atmosphere to form asolid-stated polyamide; the polyamide being solid-stated in the presenceof the metal or the metal being added to the polyamide after thesolid-stating step; the polyamide comprising an MXD polyamide, thetransition metal comprising a cobalt carboxylate compound and the cobaltbeing present in an amount of 200 to 2000 ppm in the polyamide; forminga package having at least one internal layer comprising theoxygen-scavenging composition; filling the package with an aqueousliquid having an oxygen concentration of 100 ppb or less and sealing thepackage; reducing and maintaining the oxygen concentration of the liquidbelow 100 ppb for 32 weeks; and wherein the heat treatment increases theoxygen scavenging performance of the composition by a factor of at least1.3 as compared to a composition of the transition metal and the samepolyamide prepared without a solid-stating step.
 58. The method of claim57, wherein the package is an injection molded container having atransparent multi-layer wall including the at least one internal layerof the oxygen-scavenging composition, and one or more layers ofpolyester.
 59. The method of claim 57, wherein the package is filledwith beer, juice or a tomato-based food product.
 60. The method of claim53, wherein the heat treatment increases the oxygen scavengingperformance of the composition by a factor of at least 2 as compared toa composition of the transition metal and the same polyamide preparedwithout a solid-stating step.
 61. The method of claim 53, wherein theheat treatment increases the oxygen scavenging performance of thecomposition by a factor of at least 4 as compared to a composition ofthe transition metal and the same polyamide prepared without asolid-stating step.
 62. The method of claim 57, wherein the heattreatment increases the oxygen scavenging performance of the compositionby a factor of at least 2 as compared to a composition of the transitionmetal and the same polyamide prepared without a solid-stating step. 63.The method of claim 57, wherein the heat treatment increases the oxygenscavenging performance of the composition by a factor of at least 4 ascompared to a composition of the transition metal and the same polyamideprepared without a solid-stating step.